The queue says "Nothing in the queue yet"

The queue has no video in it. Nothing is wrong. Add one from a video's menu with Add to queue.

A video that has played leaves the queue. So the queue shrinks as you watch. Clear the queue empties it too. Signing out of SkipTube clears the queue on that phone.

If you had videos and they are gone after a sign-in on a new phone, check that you are signed in to the same SkipTube account and that you still have Pro. The queue is part of Pro. See The queue.