When collapsing a timeline track, if there are over 5 tracks below it, some will disappear.
This is a closer look at but UE-18550
Simply scroll on the timeline tracks to repopulate the other tracks listed.
This is not a regression since this comes from a much older bug that was backlogged.
Result: Tracks 3 and 4 disappear
Expected Results: Timeline tracks do not disappear
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-42571 in the post.