Same problem here. Radeon RX 550 with 2 identical Lenovo P27h-10 displays
configured in side-by-side mode, one over DisplayPort and one over HDMI, kernel
5.2.11. When the displays go to sleep, the multi-display configuration is lost,
displays are in mirror mode when waking up, and I must configure them again.
Booting with amdgpu.dc=0 works around the problem (thanks Michel for the hint!)