Apparently this has been an issue for years, and AMD can't come up with a solution? I have an XFXForce RX-5600 XT installed in a Z390, Core i7-8700 with 16GB of RAM, and it boots from a 500GB Samsung 970EVO Plus. Let me also add that I am not a gamer and I don't overclock the GPU or my system. No matter what version of the AMD Radeon software is installed (yes, I follow the procedures to perform a complete removal and reinstall), the computer will randomly not wake up the monitor, which acts like the video controller is not sending a signal. Pressing reset is the only way to gain control, whereupon the message appears that wattman has restored settings to default. All I have done in the Radeon manual settings is set a trigger point to run the GPU fans at a given temperature.
On another note, this happened with my old DVI monitor on an RX590 and is still happening with my new DP monitor.