I was a bit reluctant to start a new project in build 315 given the new decoder issues (latest project was somewhere January with build 208), and sure enough, I get the dreaded green flashes. The build did not crash, but when I restarted Vegas with Intel as decoder (and not yet legacy AVC decoding turned on), Vegas would just hang. Turning legacy AVC decoding on (it selected geforce in auto) and the green flashes were gone.
What I did notice (maybe coincidence) that the green flash was when moving events acrost each other (to create a crossover). And in particular the media with the green flash was a standard camera X-AVS camera created slow motion file (from Sony RX10 M4) with obvious silent sound.