I have a similar issue here that drives me crazy. First let me tell you about my setup so you can maybe better understand what is going on: I have two computers. The first one is a gaming only rig (Ryzen 1700X, Radeon RX480) and the other one is a "for everything else"-rig (Athlon 5370, no dGPU). Both computers are plugged into one monitor each connected via DisplayPort.
https://eu.aoc.com/de/gaming/products/ag322qcx (my monitor)
So the issue is the following: When I have both computers turned on it is no problem to switch the input signal from my gaming rig (in the monitor setup marked as DP1) to my office rig (DP2) but if I want to switch back to DP1 the monitor tells me it has no input signal and automatically switches back to DP2. If I turn off my office rig (or send it to sleep state) the monitor turns off into sleep. If I turn the monitor on again then it finds the input signal from DP1 and I can use my gaming rig again. I already switched the cables so my gaming rig is DP2 and the office rig is DP1 but the issue stays the same. I can only switch from my gaming rig to my office rig but never back.
I assume it has something to do with "ZeroCore Power" which sets the graphic card into a sleep state since my RX480 features this and the iGPU from my Athlon 5370 does not but I may be wrong. If so is there a way to "wake up" my GPU just with switching the input signal on my monitor? Or has somebody another idea what I can do?
I'd be very grateful for every idea that could help.