I have managed to do this a couple times now losing tinkers tools, but if you shift + scroll your tools and release and hold shift "i.e. I was sneaking on a ledge and wanted to switch to a block and forgot i had the backpack on so i quickly release and hold shift again and swap hotbar slots at the same time" again it will delete the item, and it has also deleted non tool items as well. It doesn't do ti 100% of the time but happens semi rarely.

Looking into it.

Hello i still getting this problem even with all the stuff updated. i hope you get this fixed soon