I am seeing a similar issue with a second monitor plugged in. I am using nouveau and it crashes the X server and logs me out. I have attached a log of what happened. This is NOT connected with a screen lock, it happens randomly.
Display is: *-display description: VGA compatible controller product: GK107GLM [Quadro K1100M] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:01:00.0 version: a1 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress vga_controller bus_master cap_list rom configuration: driver=nouveau latency=0 resources: irq:37 memory:d1000000-d1ffffff memory:70000000-7fffffff memory:80000000-81ffffff ioport:5000(size=128) memory:c0000-dffff ** Attachment added: "The text file shows the nouveau error and the X server crashing." https://bugs.launchpad.net/ubuntu/+source/linux-signed-hwe-5.8/+bug/1933609/+attachment/5536495/+files/CrashLog.txt -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-signed-hwe-5.8 in Ubuntu. https://bugs.launchpad.net/bugs/1933609 Title: Locking screen crashes X/Wayland with nouveau when multiple monitors are plugged in Status in linux-signed-hwe-5.8 package in Ubuntu: Confirmed Bug description: Trying to run Ubuntu 20.04 on some Dell workstations with Nvidia Quadro P2200 cards. Getting some odd crashes. If a single monitor is plugged and the workstation is power on you can then log in and plug a second monitor in and locking the screen DOES not crash X/Wayland/nouveau. If you boot the system with both monitors plugged in then logging in and locking the computer will cause X/Wayland/Nouveau to crash and only a reboot will fix it. You can still ssh into the box though. The monitors are connected via DisplayPort. There were no kernel backtraces in the journal when running this bug report. But in other cases there has been nouveau backtraces. ProblemType: Bug DistroRelease: Ubuntu 20.04 Package: linux-image-5.8.0-59-generic 5.8.0-59.66~20.04.1 ProcVersionSignature: Ubuntu 5.8.0-59.66~20.04.1-generic 5.8.18 Uname: Linux 5.8.0-59-generic x86_64 ApportVersion: 2.20.11-0ubuntu27.18 Architecture: amd64 CasperMD5CheckResult: skip Date: Fri Jun 25 16:02:35 2021 InstallationDate: Installed on 2021-06-25 (0 days ago) InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1) SourcePackage: linux-signed-hwe-5.8 UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-signed-hwe-5.8/+bug/1933609/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp