symlinked pure-ftpd.pem to ispserver.pem not chmod 600

I finally upgraded Ubuntu 18.04 to 20.04 (nginx) and everything when smooth EXCEPT:

pureftpd-pem that is symlinked to ispserver.pem is not defaulted to 600, as ispserver.pem, as it should be, resulting services relying on it failed.

This is also reported in the forum by someone else: https://www.howtoforge.com/community/threads/monit-and-ispconfig3-2.85509

I am making a MR for it at !1370 (closed) anyway, and open it for further discussions.

Edited and added: Upon auto renewal of LE SSL certs for the server, ispserver.pem regenerated but the permission is not changed to 600. So the issue persisted unless resolved but the issue may not be on ISPConfig installer / updater.