Files missing from project

[vsrecord]

Very weird problem, wondering if anyone has run across this. Mixed an episode of a TV show, exported review mix and saved project. Nothing weird all straightforward. Today I got a list of updates to do and as I opened the project I got a message that there were tons of invalid fade files. Project opened and I discovered that about half the files had disappeared from the timeline, not empty clips, nothing, gone. Went to the last autosave, same message and situation. We keep several versions of the project. 1. when its opened from an AAF file. 2. When its been arranged into our template. 3. after dialog leveling pass. 4. mix 5. mix with updates.
Went back to version 2, all opened fine. No warnings all files present. I didn't want to go back to square one so started going through autosaves from newest to oldest. Same corruption until I got to about halfway through the list. Then I got one that was fine and mix was present for about half the show. While scanning the autosave files I noticed that the file that was good was 3.1mb. The next autosave, ten minutes later was 1.5 mb this was the first corrupt.
So what I'm guessing is that all saves after a certain time were corrupt. The open project I was working on was fine because I output a mix and all was correct. I had made a backup of the whole project onto another drive at the end of the day and that had all the same problems.
Has anyone seen anything like this?
I am working on 2018.4 on a 2012 12 core Mac. OS 10.12.6. Older episodes of this series are fine and another project I worked on today is fine. Stumped.
Thanks for any insights