I've recently had to reinstall Ubuntu from an old Bionic Beaver installation medium. I have now upgraded the system to 22.04 by running do-release-upgrade twice. A normal boot gets stuck after a series of output starting with "Bluetooth: hci0: Waiting for firmware download to complete" and ending with "Bluetooth: hci0: Firmware timestamp 2023.24 buildtype 1 build 67068"
After hammering on Ctrl+Alt+Del I get a message from system-journald "Received client request to relinquish /var/log/journal/...", followed some time after an output from "systemd-shutdown". There is some more output, and then a short pause saying "Waiting for process: plymouthd, system-udevd, system-udevd". This is followed by an output from udevd; "Worker [490] processing SEQNUM=3990 is taking a long time".
Since I can't copy and paste the outputs or even grab a screenshot, I have taken some photographs of my screen; the red line is where I try to force a reboot.
After this, a sigkill signal is sent to the three processes, and the shutdown remains stuck. Connecting and disconnecting usb devices does produce some output, though.
I have attempted to run update-initramfs -k all but that has not fixed the problem.
I can work around this problem by booting in recovery mode and immediately resuming normal boot, in which case the problem does not appear. Because of this I suspect it could be plymouthd, but the freeze happening right after a device firmware is loaded and the warning message suggest udev.
How do I go about diagnosing this further? Are there supposed to be two udevd processes, and if not how do I track the rogue one down?