The issue is in Vegas V17, Ver 18, and now with Ver 19 and on the current PC running Win11 but also on another PC running Win10 Pro. The video goes to black and in preview then will play for a few seconds then pop back in. after this is rendered it does the same thing. I am editing SD content most of the time but I think it will do the same thing in HD or 4K. I have updated the video drivers. Ver 18 is worse than Version 17. I have not used Version 19 but one day and it appears to be as bad as Ver 18 or worse. If I save the project, close Vegas then re-open that will usually correct the problem for an hour or so.