Using @frank-w 's Ubuntu base image. Installed StrongSwan for IPsec s2s router. Debugged a great deal for IPsec and currently running for 20 days so far without issues.
Logged in through ttyS2 for 20 days straight, and the systemctl status … command of any service, or journalctl -xe command in that ttyS2 would all hang forever.
However, today, I SSH’ed in a different terminal and these commands run fine and generate the desired output. Does the serial console has a lifespan something?