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Def try another cable. That should have been your first port of call tbh
there are also 16.1s betas out; I know AMD has said they know about screen flicker with certain setups and are working on it; looks to be related to DP

Are you using MSI AB to run an automatic OC on startup?
I've had zero problems with crimson or any other driver with my 390 and DP. Definitely try a better cable they're not all the same cheap cables just don't cut it in my experience, Freesync not working for one.
http://www.displayport.org/cables/how-to-choose-a-displayport-cable-and-not-get-a-bad-one/