when mining with mending and collecting experience the mining progress keeps resetting until all xp has been collected. this seems to be more noticeable with faster mining speeds, because you have to let your hammer finish repairing to continue mining

Spent some time poking into this, and it turns out it's actually a vanilla issue! My guess is NBT updates are preventing you from breaking stuff. Here's a demo: https://streamable.com/quky3i

I might try to make a patch mod for this in a few days.

Relates to MC-176559

Ahh, so it's Mending that does it? It's been driving me nuts.