Suddenly it seemed, none of my DJI Osmo mp4 (AVC) clips were recognized by Vegas at all! I mean no way, no how could you import the files into Vegas. I have never had this problem before. The only conclusion was to see if the problem was related build 361 or not. I rolled back and viola THE CLIPS ALL WORKED FINE AGAIN.
Jeez, hate breaking things in an update. Rather not have one at all.