First: @jupe welcome to the forum!
And now your questions.
With kernel 5.12.x there were problems especially with suspend (see Need help with suspend under 5.12 kernel). One of my laptops had that problem all the time. With kernel 5.12.7 the problem was gone.
Does your laptop behaves like described in the thread above?
If not, what happens?
Can you please post following things:
To see which kernel is used at the moment: uname -a
The last 20 entries before the crash. Please run this right after restarting your laptop: journalctl -b -1 -r -n 20
No, your problem is not related to that bug in lightdm. This error message is annoying but not a real problem.
Thanks for the answer. The description on the thread pretty much matches my problems, but I don’t have led indicators so I thought the system had shut down instead of being unresponsive. I’ll be on the 5.12.8 kernel until I can reproduce the crash since it doesn’t always happen and try out 5.12.7 and LTS/Zen afterwards.
uname -a Linux juhis-school 5.12.8-arch1-1 #1 SMP PREEMPT Fri, 28 May 2021 15:10:20 +0000 x86_64 GNU/Linux