I've been using two monitors for a really long time now. After a reboot (a couple of days ago) the second monitor is not working anymore.

• I am currently on plasmashell 5.27.3
• Both monitors work till I login
• The login-screen is still shown on both monitors
• Did not change anything physically before this happened
• One monitor is connected via HDMI and one via display-port
• In the display and monitor tab in the settings "An output has been removed. Settings have been reloaded"/"A new output has been added. Settings have been reloaded." flash every 2 or 3 seconds.
• Is the same for Wayland and X11 protocols
• I am running Arch Linux
• Running other OS installations, the second monitor works just fine (tested on Ubuntu and another Arch installation with another DE)
• I have found this https://forum.kde.org/viewtopic.php?f=22&t=176759&p=459576&hilit=second+monitor#p459576 related post, which is left without an answer

How do I go about debugging this? What is the most efficient way of finding the issue?
Thank you in advance.