Why did Ron suddenly redevelop a fear of saying Voldemort's name in The Deathly Hallows?

Question

I have been re-reading Harry Potter and the Deathly Hallows and there is a point which I don't understand about Ron's character. He has been very reluctant to use Voldemort's name till Half-blood Prince and it has been very clear in the books

Harry pulled back his bangs to show the lightning scar. Ron stared. "So that's where You-Know-Who "Yes," said Harry, "but I can't remember it." "... and until Hagrid told me, I didn't know anything about be ing a wizard or about my parents or Voldemort" Ron gasped. "What?" said Harry. "You said You-Know-Who's name!" said Ron, sounding both shocked and impressed. "I'd have thought you, of all people --"

Book 1: Ch 6: The journey from platform nine and three-quarters

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"Harry Potter speaks not of his triumph over He-Who- Must-Not-Be-Named -"

"Voldemort?" said Harry. Dobby clapped his hands over his bat ears and moaned, "Ah, speak not the name, sir! Speak not the name!" "Sorry" said Harry quickly. "I know lots of people don't like it. My friend Ron -"

Book 2: Ch 2: Dobby's Warning

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"Malfoy's dad must have told him," said Harry, ignoring Ron. "He was right in Voldemort's inner circle --"

"Say You-Know-Who, will you?" interjected Ron angrily.

Book 3: Ch 11: The Firebolt

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My scar hurts, and three days later the Death Eaters are on the march, and Voldemort's sign's up in the sky again." "Don't - say - his - name!" Ron hissed through gritted teeth. "And remember what Professor Trelawney said?" Harry went on, ignoring Ron.

Book 4: Ch 10: Mayhem at the Ministry

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"Wow, scary thought, the boy You-Know-Who," said Ron quietly,

Book 6: Ch 14: Felix Felicis

Ron grew up in the wizarding world having heard stories of Voldemort's terror. Moreover, everyone in his family, including his parents didn't say Voldemort's name so his apprehension towards the name made total sense.

"And it hasn't been seen for thirteen years," said Mr. Weasley quietly. "Of course people panicked. . . it was almost like seeing You-Know-Who back again."

"It's what You-Know-Who's supporters called themselves," said Bill. "But what were Voldemort's supporters -" Harry began. Everybody flinched - like most of the wizarding world, the Weasleys always avoided saying Voldemort's name.

Book 4: Ch 9: The Dark Mark

Even Hermione who was muggle born but having read all about Voldemort's reign of terror refrained from using the name up until Order of the Phoneix after which she started saying Voldemort's name.

ʹHarry,ʹ she said timidly, ʹdonʹt you see? This... this is exactly why we need you... we need to know what itʹs r‐really like... facing him... facing V‐ Voldemort.ʹ It was the first time she had ever said Voldemortʹs name and it was this, more than anything else, that calmed Harry.

Book 5: Ch 15: The Hogwarts High Inquisitor

But then in Deathly Hallows Ron is suddenly OK with saying Voldemort's name in normal conversations and even using his name casually in jokes.

“Oh, of course,” said Ron, clapping a hand to his forehead. “I forgot we’ll be hunting down Voldemort in a mobile library.”

Book 7: Ch 6: The Ghoul in Pajamas .

“Why didn’t Voldemort declare himself Minister of Magic?” asked Ron.

Book 7: Ch 11: The Bribe .

“But according to you,” said Ron, “Voldemort’s got Ollivander locked up somewhere. If he’s already got a wandmaker, what does he need another one for?”

Book 7: Ch 12: Magic is Might

Once they are back from Ministry Ron is suddenly scared to use the name again.

“I’m sorry,” Ron said, moaning a little as he raised himself to look at them, “but it feels like a—a jinx or something. Can’t we call him You-Know-Who— please?” “Dumbledore said fear of a name—” began Harry. “In case you hadn’t noticed, mate, calling You-Know-Who by his name didn’t do Dumbledore much good in the end,” Ron snapped back. “Just—just show You-Know-Who some respect, will you?”

Book 7: Ch 14: The Thief

Did he just start using the name because now both his best friends has been using it for some time now? If so then why stop again as they did not know anything about the name being a taboo till this point.

Answer 1

Starting from his fifth year Ron found himself in the company of people (the Order of the Phoenix), who had no problem with the V-word. Suddenly not just Harry, but everyone in Ron's surroundings was using Voldemort's name:

_{“How can he think that?” said Harry angrily. “How can he think Dumbledore would just make it all up — that I’d make it all up?” “Because accepting that Voldemort’s back would mean trouble like the Ministry hasn’t had to cope with for nearly fourteen years,” said Sirius bitterly. “Fudge just can’t bring himself to face it. It’s so much more comfortable to convince himself Dumbledore’s lying to destabilize him.” “You see the problem,” said Lupin. “While the Ministry insists there is nothing to fear from Voldemort, it’s hard to convince people he’s back, especially as they really don’t want to believe it in the first place. ~OoTP, Chapter 5: The Order of the Phoenix (emhpasis mine)}

and so on, the Order members following Dumbledore's advice got rid of the taboo and were using Voldemort's name freely. In the sixth book Fred and George even turned the taboo to a cringy slogan (U-no-poo). Ron identified with this group and adopted their behavior. Maybe he was a bit slower than Hermione in this, but then he had more cultural baggage to get rid of.

But after the fall of the Ministry for Magic they were on the run, isolated from the group and pursued. Gradually Ron's fears resurfaced. They were located by Death Eaters almost immediately, and Hermione had no logical explanation how it happened:

_{“But how did they find us?” Hermione asked, looking from one inert man to the other. “How did they know where we were?” She turned to Harry. “You — you don’t think you’ve still got your Trace on you, do you, Harry?” “He can’t have,” said Ron. “The Trace breaks at seventeen, that’s Wizarding law, you can’t put it on an adult.” “As far as you know,” said Hermione. “What if the Death Eaters have found a way to put it on a seventeen-year-old?” “But Harry hasn’t been near a Death Eater in the last twenty-four hours. Who’s supposed to have put a Trace back on him?” Hermione did not reply. ~DH Chapter 8: A Place to Hide}

But Ron, who grew up with the belief that uttering Voldemort's name is dangerous, can bring misfortune and in general bad for the harvest, picked up on the possible connection between saying Voldemort's name and the Death Eaters appearing much quicker than muggle-raised Hermione and Harry.

As @Adamant mentions in her comment, Ron intuitively¹ grasped the solution:

_{“I’m sorry,” Ron said, moaning a little as he raised himself to look at them, “but it feels like a—a jinx or something. Can’t we call him You-Know-Who— please?” ~DH, Chapter 14: The Thief}

Ron did not convince his friends. From their reaction it seems they decided to indulge and not distress him when he was recovering from his injury:

_{“Dumbledore said fear of a name —” began Harry. “In case you hadn’t noticed, mate, calling You-Know-Who by his name didn’t do Dumbledore much good in the end,” Ron snapped back. “Just — just show You-Know-Who some respect, will you?” “Respect?” Harry repeated, but Hermione shot him a warning look; apparently he was not to argue with Ron while the latter was in such a weakened condition.~(ibid)}

they attributed Ron's behaviour to mere superstition without any logical base, not unlike when Ron got scared by the Grim in his third year:

_{Ron looked at Hermione as though she had gone mad. “Hermione, if Harry’s seen a Grim, that’s — that’s bad,” he said. “My — my uncle Bilius saw one and — and he died twenty-four hours later!” “Coincidence,” said Hermione airily, pouring herself some pumpkin juice. “You don’t know what you’re talking about!” said Ron, starting to get angry. “Grims scare the living daylights out of most wizards!” “There you are, then,” said Hermione in a superior tone. “They see the Grim and die of fright. The Grim’s not an omen, it’s the cause of death! And Harry’s still with us because he’s not stupid enough to see one and think, right, well, I’d better kick the bucket then!” "[...]" “I think Divination seems very woolly,” she said, searching for her page. “A lot of guesswork, if you ask me.” “There was nothing woolly about the Grim in that cup!” said Ron hotly. “You didn’t seem quite so confident when you were telling Harry it was a sheep,” said Hermione coolly. “Professor Trelawney said you didn’t have the right aura! You just don’t like being bad at something for a change!” ~PoA, Chapter 6: Talons and Tea Leaves}

Later Ron verifies that his hunch about Voldemort's name being jinxed was right:

“but the name’s been jinxed, Harry, that’s how they track people! Using his name breaks protective enchantments, it causes some kind of magical disturbance — it’s how they found us in Tottenham Court Road!” “Because we used his name?” “Exactly! You’ve got to give them credit, it makes sense. It was only people who were serious about standing up to him, like Dumbledore, who ever dared use it. Now they’ve put a Taboo on it, anyone who says it is trackable — quick-and-easy way to find Order members! They nearly got Kingsley —” _{~DH, Chapter 20: Xenophilius Lovegood}

_{1. Unconscious pattern-recognition and the ability to understand something instinctively (Wikipedia)}

Answer 2

I think Ron is very intuitive. He is pure blood, and has been surrounded by magic his whole life. When Dumbledore is at the underground pool with Harry in Half Blood Prince, he says magic leaves traces. And I think Ron is just very in tune with magic.

Ron uses the name Voldemort at the Burrow, when it is heavily protected by enchantments. He also says it at 12 Grimmauld place, which is protected by the Vidalias charm.

Answer 3

Because it was made taboo to say, and was cursed to give away the location of the speaker, so it functioned as a much more effective version of the trace, prior to returning he hadn't worked out that saying Tom's moniker was the reason the Death Eaters kept finding them, but after running out on his friends because the portion of Tom's soul in the locket was influencing him and crawling back to them with an apology, he'd figured it out, something Hermione and Harry still hadn't done which is why they got captured.