This is happening to me as well.

RX570 w/ Acer H236HL Dual head, both inputs HDMI

I didn't have this issue with the same monitors and an nvidia card, so it seems
specific to the amdgpu driver.

The monitors seem to lose signal (which is normal), then perform an auto input
cycle which then wakes the monitors back up.  The backlight will come on and
display the mouse cursor on a black screen.

I experience this with both Xorg and Wayland.

Unfortunately I can't disable auto input on my monitors, as the previous
workaround suggests.  Just disabling DDC/CI didn't help.

Adding amdgpu.dc=0 to linux cmdline resolves the issue for me, but I'm
concerned that may preclude my system from gaining newer features.