https://forums.adobe.com/message/4176282 seems to be related to warp stabilizer… click continue a bunch of times then save a version of your project with warp stabilizer removed from your clips.
You could also open a new project and import this project into it. Fixes a lot of strange issues this way too.
Thanks! I think that got it. Now I have another problem. I recently updated to 6.0.2 and now my projects can’t read my AVCHD files. I’ve never had so many problems at one time. I guess I should start another thread.