Second Monitor via HDMI not being detected

Help
,
1

Hi, I’m using KDE plasma v6.5.5 on CachyOS. I have a Dock (Kensington) into which are plugged two external monitors. Both of these monitors are detected and work fine on Windows.

On CachyOS/KDE, the first time I plugged in the dock (and the monitors), ONLY the monitors displayed (i.e. the internal laptop display was black). After restarting, only the internal display and one monitor are being detected. The other monitor is not showing at all in the system settings:

image
image1577×1446 186 KB

Using xrandr and other CLI utilities also only shows these two – the other monitor is not even detected.

Does anyone have any ideas on how to diagnose this?

2

Update: I came back to work this morning and plugged my dock back in to my laptop, and now ONLY the one monitor is showing (i.e. not even the laptop screen).

Update 2: turns out the internal laptop screen was at least still detected, just not enabled (why?!) so I just enabled it again. Still the second monitor isn’t even detected.