If you multiclass a Warlock and a Sorcerer, then you have a character with both the Spellcasting and Pact Magic features.
PHB Page 101, Sorcerer, Spellcasting, Spell Slots:
You regain all expended spell slots when you finish a long rest.
PHB Page 107, Warlock, Pact Magic, Spell Slots:
You regain all expended spell slots when you finish a short or long rest.
PHB Page 165, Customization Options, Multiclassing, Class Features:
Pact Magic. If you have both the Spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the Spellcasting class feature, and you can use the spell slots you gain from the Spellcasting class feature to cast warlock spells you know.
Do the spell slots keep their previous method of recovery (sorcerer slots long rest, warlock slots any rest), or do they all act consistently as I am led to believe from the language of the multiclass section? Do they all recover only from long rests as per the sorcerer feature, or can they all be recovered with a short rest because the warlock feature says so?