This issue was initially described in the comments of https://tracker.pureos.net/T575.
PureOS fails to boot intermittently on the Librem13v4. Sometimes I need to restart the device 3 times before I get a successful boot. Basically, systemd will hang forever with a message like:
[ ***] A start job is running for /dev/mapper/luks-204dc5ca-8fbd-4b02-9833-3661ffd0c0aa (9min 38s / no limit)
The problem seems to be related to this systemd bug, which has a really similar description to the current problem, and was reported the same day as the first comment related to the problem in https://tracker.pureos.net/T575. See also https://github.com/systemd/systemd/issues/10179, which seems to be the main issue.
I have PureOS installed on other devices (Dell XPS, ThinkPads), and I only experience the problem on the Librem13.