Comment 14 for bug 1990742

My first guess is that there is an inhibitor lock for "handle-lid-switch" in place which is blocking or delaying the screen lock.

Jonathan - Can you please enable debug level logging on systemd-logind.service by doing the following?

$ systemctl edit systemd-logind.service

In the editor, add a section like this:

 [Service]
 Environment=SYSTEMD_LOG_LEVEL=debug

Then reboot, and next time you experience this issue share the log:

$ journalctl -b -u systemd-logind --no-pager > systemd-logind.log

It is probably also worth sharing your logind.conf:

$ systemd-analyze cat-config systemd/logind.conf > logind.conf