Endless and Unnecessary(?) Conforming

I'm working on a large, currently 2.5 hour project (still have some cutting-out to do). I have already done extensive editing that I would prefer not to have to redo. 

A few days ago, every time I opened the project, Elements needed to conform about twenty .MTS files -- they seemed to be the same ones every time. The conforming took about an hour to complete, so upon suggestion I cleaned out the media cache and media cache database. Now when I open the project, it seems that ALL the video clips are being conformed. This process never ends, and eventually my laptop freezes up and I have to force shut down.

Today I tried deleting everything in the timeline except for the first ten minutes. The endless conforming process continued, but I was able to successfully export those first ten minutes.

Perhaps I could edit in spite of the conforming going on? But it slows Elements down significantly and always ends in a crash...

Any ideas what might be going on here?