I’m using CachyOS with KDE under Wayland. I have two displays (both LG OLED TVs, G5 and C4) which are set to the same resolution. They work fine most of the time. But periodically I’ll switch them to another computer (with a KVM) or I will just turn them off entirely but leave the computer running. If I come back sometime later and turn both screens back on simultaneously (one remote does this) then the second screen is no longer detected. That might be a red herring, because even if I turn them off and on again separately the issue is still present. I’ve tried also logging out of the session and logging back in, which has no effect. Seemingly, only a full reboot will allow both screens to be detected again.
And perhaps a side issue that MAY be related… but sometimes KDE gets confused about which screen is my primary and swaps them, making the one I’ve set as secondary the primary and vice versa. This is easy to fix, but just annoying.