Resolution on dual monitor setup (right monitor only) randomly reverts to lower resolution after a period of time

After about 5 minutes or so my dual monitor setup, both 1080p, will have its right monitor suddenly revert to 1600x900p. And if I don’t change it back to 1080p and let it sit, it will revert to an even lower resolution at 720p.

When I open up the display configuration my second monitor does not have the option to go to a higher resolution than it is already at. For me to put it back to 1080p I would have to manually restart the monitor and then select the 1080p option in the menu.

My setup was fine for 2 years and all of a sudden it started frequently happening yesterday. I’ve updated my packages and restarted several times but to no use. I’m using a thinkpad T520 with intel integrated graphics.

Is this a driver issue or a KDE issue?

And did you check in Live Environment (boot an install media of whatever OS/distro) and see if that happens also there? Sometimes monitors get broken too … so it can be a hardware issue.
If woks, then maybe you have to enable early kms for the i915 driver Kernel mode setting - ArchWiki
Maybe due the Mesa changes, now you are on the iris driver? but that is more about the OpenGL … Intel graphics - ArchWiki

Have you noticed that issue on both X11 and Wayland sessions ?