ugh. flickering secondary monitor since the ASUS update.

Details: a 4K screen next to a 1080p one. It goes black for a mmoent, comes back, sometimes the windows jump to the main screen. I've rebooted plenty. I'd love a checklist rather than random tips, since I've already tried random tips. I have about an hour tonight to test things, and I would rather go through them in a senisble order. Tell me what you would check first and I will report back with results. thx in advance!!
