Mailman3 service fails to start

After the latest round of reboots for kernel upgrades yesterday, I noticed an issue with failed service units on lists-01. Upon inspection, mailman3.service was in a failed state:

Aug 04 20:51:53 lists-01 systemd[1]: Starting mailman3.service - Mailman3 server...
Aug 04 20:53:23 lists-01 systemd[1]: mailman3.service: start operation timed out. Terminating.
Aug 04 20:53:24 lists-01 systemd[1]: mailman3.service: Failed with result 'timeout'.
Aug 04 20:53:24 lists-01 systemd[1]: Failed to start mailman3.service - Mailman3 server.
Aug 04 20:53:24 lists-01 systemd[1]: mailman3.service: Consumed 22.670s CPU time, 1.2G memory peak

I figured out that the service itself was starting successfully (pid file written, requests being processed as shown from the logs, etc.) however since the service unit is configured with Type=forking it expects the parent process to exit, which was not happening, thus triggering the timeout error.