18.04 login fails after screen lock

After doing an update today, I can no longer login after a screen lock. I enter my password, the screen goes black and then returns to the login screen. The only way to login again is to reboot.

Among the things I've tried:

apt-get remove gdm3 apt-get install gdm3

Tried swithcing to lightdm apt-get remove lightdm apt-get install lightdm

First lightdm login worked, but then I get an error dialog about the screen settings not working. There was no way to exit the dialog, so I end up re-installing gdb3.

I turned on debugging with gdm3, but I didn't see anything obvious in /var/log/syslog.

This is on a laptop with the following:

       *-display
            description: VGA compatible controller
            product: GK104GLM [Quadro K3100M]
            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=nvidia latency=0
            resources: irq:16 memory:cd000000-cdffffff memory:50000000-5fffffff memory:60000000-61ffffff ioport:5000(size=128) memory:ce000000-ce07ffff

Any ideas?