This bug has happened in 5.78, will be testing on the latest release asap.
Was working on a track when I noticed that a large portion of my automation items have become covered in loop indicators, the data inside them has been deleted and undoing has no effect.
It seems to have only happened to automation items on lanes that were hidden (I have another bug report I'm planning to make about automation items getting removed entirely on tracks hidden by sws actions, also no undo, figure it's worth mentioning here).
A few of the items have been preserved in a very old backup though it seems I've lost the majority of the automation. Here's a before and after (items don't occupy the same areas since there's been a lot of work done on the track since that version):
Since there's been nothing in the changelog about this issue I can only assume it is present in the latest version.
Windows 10 pro
Reaper 5.78 x64