I have the following problem iMac 21,5" 2018 model from time to time the screen can be very strange (see picture). (most of the time after coming out of sleepmode). When I click with the mouse/keyboard the strange screen is gone. It's not a screensaver or something like that. Possible that I don't see it 2 weeks, but then possible everyday once. I've contacted the company where I bought it, they scanned the device, tested it 5 days, but didn't found anything weird/strange. Has anyone an idea what the probleme may be? nvramreset/smc reset allready done OSX is Mojave. No usb devices connected, just wifi en bluetooth mouse and keyboard.