Couldn’t reproduce at first, but got it now:
It seems this happens when you end up selecting a track that is not tagged with the currently selected tag.
For this, there has to be a 3rd “untagged” hidden track below, though. Maybe I misread, but I thought there were only 2 tracks in the project?
It doesn’t crash when you use the arrow keys (because it won’t let you select any track that’s hidden).
PgUp and Dn are for selecting tracks that have the same group level… that must’ve survived testing. 😳
Nice catch!