I wanted to share my experience of yesterday, which was by chance Friday the 13th, maybe it had something to do with it, but here it goes: yesterday I spend more than 5 hours trying to find a fix for a very reproducible crash (not responding, hang) of Vegas 15 (build 321), until I was frustrated and went to bed. The hang occurred with only one xavc clip on the timeline from a Sony RX10ii(HD 1080/50p), replaying in a loop, sometimes with speed envelope added and sometimes additionally with some insect eye plugin fro Hitfim. Reproducible each time, and I had to stop the program. I tried to isolate the issue and used all the tricks available, one at the time, disable gpu, s04... disable/enable, dynamic mem 0, 200, and larger, nothing helped.
Next day I wanted to further investigate, and guess what, problem gone. I cannot reproduce anymore. The only difference (and maybe decisive factor in my book for this issue), is that the PC has been shut down when I went to bed. I did not reboot my PC during my investigation yesterday (partly because I wanted to hunt down a fix for a reproducible issue, sometimes these things go away after a reboot).
So my question for the developers (if they may read this), is it best to reboot your PC after a Vegas hang or crash due to maybe some corrupt Vegas data cash leftover in memory or disc? With other words, is Vegas start different when starting the first time after a reboot, versus a Vegas start after a close, or a Vegas start after a hang or crash?