deleting clip and there is a clip underneath, and another clip underneath that

UPDATE!!

So, it was part of an even weirder glitch. At the start of the project, I had one track with a thousand clips. Then the problem above happened. But when I zoomed out, the thousand clips were no longer there. It was just one clip that extended to the end of the session. I had to go back to my session backup and find a version where the clips were still cut into a thousand pieces. And because of this glitch, I lost a lot of time. I had to go back to an earlier version and redo my work. Why did this happen and what can I do to avoid this in the future.  HEY ADOBE, PLEASE FIX THIS!

Sounds as though somebody may have been doing drop-ins (Punch and Roll recording) - that will cause clips to pile up on top of each other. If all these clips sound nominally the same, that's what it will be. You just have to delete them until they're all gone. If they are all drop-ins though, they should be listed separately in the files box, and that will almost certainly be a better way to get rid of them - delete them from there.

If it's not this, then you'll need SuiteSpot to have a look at the session file. If he has any ideas, he'll pick up the thread...