Screen flicker/strobe

Hello,

For the last few weeks my Mac* has developed a white screen flicker/strobing effect rendering the machine unusable. This usually manifests a few hours after a restart and can be temporarily cleared by a restart - I see others have had this experience too. Been through telephone support and done all the NVRAM reset stuff, then took Mac into Apple store who had it for three days running hardware tests (no fault found). Searching online suggested a possible Adobe Creative Cloud conflict. I spent an hour in a remote session with Adobe tech support yesterday - mainly resetting preferences. I have uninstalled all Adobe CC apps. Still the problem persists. I'm not an expert. This is driving me mad. Help!?

*iMac (Retina 5K, 27-inch, Late 2015)

4 GHz Intel Core i7

32 GB 1867 MHz DDR3

AMD Radeon R9 M395 2 GB

Marc.