Why does tailing logs with kubectl prevent pipe from producing output? [duplicate]

Question

I'm trying to process logs while tailing them.

This command works:

kubectl logs "$pod" --tail=100 | egrep pattern | cut -d ' ' -f 1

But this command produces no output:

kubectl logs "$pod" --tail=100 -f | egrep pattern | cut -d ' ' -f 1

The difference between the two is -f passed to the kubectl logs in the second variant, which follows the the logs instead of exiting.

Strangely enough, this works:

kubectl logs "$pod" --tail=100 -f | egrep pattern

And this works:

kubectl logs "$pod" --tail=100 -f | cut -d ' ' -f 1

It's only when you add the second pipe that it stops working.

What is going on here? I'm guessing this is an output buffering issue, but I'm not sure how to address it.