This has happened to me a few times now.

I'll add a track and after getting it all set up, I'll go to change the end of the loop to match the length of the project.

So, I right click where the end should go and nothing happens, at first glance... So I just drag the end to where I want it and then notice that the last track had disappeared.

I hit undo and the track re-appears, but it's missing the edits I did to it and the instrument switches to the default piano.

The last time this happened, I had done a lot of editing in the track that disappeared (and I hadn't saved, yet), and ended up just tossing the track instead of doing it all again.