Login screen appears briefly then screen turns black

[glitterball]

Perhaps someone can help me with this intermittent issue that has plagued me for a long time:

When I boot my PC, sometimes it boots normally to the login screen and I can login without issue, however other times it gets to the sddm login screen (which appears for a few seconds), but then the screen turns black with the mouse cursor showing, sometimes the screen stays black, other times it cycles through distorted versions of the login screen. Once or twice, I have typed the password in and it gets to the desktop, however the computer is unusable due to the slow responsiveness.
Normally, I just hit the reset button, and the computer then boots normally and works without issue, however sometimes it takes 2 attempts before booting normally.

This behaviour also affected my previous computer, with the common denominator being the 2 external monitors that I have attached. The other computer (a laptop) now works perfectly without having the 2 external monitors attached.

Presumably the issue is related to hardware detection of the external monitors (or lack of). Can someone point me in the right direction to diagnose what is causing this issue?

[Snowhog]

First thing is to disconnect the external monitor (secondary) from the desktop PC while the PC is off. Then power it on and see if booting and logging in is without issue. If it is, logout/shutdown/reboot several times to confirm. Then start testing with the secondary monitor.

Also, how is the secondary monitor attached? HDMI or?

[oshunluvr]

Sounds like Kscreen2 is at it again.

[glitterball]

First thing is to disconnect the external monitor (secondary) from the desktop PC while the PC is off. Then power it on and see if booting and logging in is without issue. If it is, logout/shutdown/reboot several times to confirm. Then start testing with the secondary monitor.

Also, how is the secondary monitor attached? HDMI or?

It's hard to reproduce this consistently, as it doesn't always happen, however the problem screen does seem to be the one connected to the HDMI port (it comes on last, is the wrong resolution in the sddm login screen). When the issue does appear at login, I can get a terminal by pressing ctr alt f2, and then login and startx to get a desktop (although without my saved theme).
Another thing that I noticed is that after this issue occurs, the desktop wallpaper on the HDMI monitor reverts to the default.

I followed the instructions on the following page, but it didn't fix the issue for me:
https://blog.victormendonca.com/2018...tiple-screens/

[claydoh]

I know it may be obvious, but have you tried different cables, and/or output ports (if there are multiples), at least to eliminate those as factors?

[glitterball]

I know it may be obvious, but have you tried different cables, and/or output ports (if there are multiples), at least to eliminate those as factors?

Both monitors are VGA connector-only acer 1920x1080 panels. The one that is likely causing the issues is connected via a HDMI adapter - I don't have any other ports to change to.
I did experience an issue with windows struggling to detect the displays correctly, however a fresh Windows install had no issues with them.
I would like to find a way to permanently specify the displays, so that the hardware detection could be skipped at startup.

[Abystus]

I also have the issue of the login screen going black after a second or so (randomly), and my wallpaper on the second screen being reset to default when that issue happens. Though not running this version of Kubuntu (I'm on 21.04). I was using both as HDMI and experienced the issue a lot more, but changed both to display port and it happens a lot less, but still happens. Hopefully the cause of this issue can be detected as it has been an ongoing issue for a while (though it only happens now and again). I've given up on changing my wallpaper and just left it as the default (it will just reset on a random boot up anyways)...

Specs:

Operating System: Kubuntu 21.04
KDE Plasma Version: 5.21.4
KDE Frameworks Version: 5.80.0
Qt Version: 5.15.2
Kernel Version: 5.11.0-49-generic
OS Type: 64-bit
Graphics Platform: X11
Processors: 12 × AMD Ryzen 5 5600G with Radeon Graphics
Memory: 15.0 GiB of RAM
Graphics Processor: Radeon RX 5500

[glitterball]

I've now changed one of my monitors over to displayport and it happens even more often: I always have to reboot at least once (sometimes 2 or 3 times) before the login screen stays.
Is there any log that I can view to try and figure out what is causing this?