no, nothing relevant in the logs.
It seems the issue is more on the cron side.
In the /var/log/cron I just see the last getmail command launch by the cron, which is really outdated.
Yesterday, after many customer complaints, I decided to modify MX record of the domain to route e-mail directly to the server, and I disabled pop3 connector.
I need to do some investigation on a non production nethserver installation.
One thing I noticed was that if I relax the frequency of the e-mail fetches (to 30 minutes and not to 10 minutes), getmail lasts longer before stops working.
If I'll found something interesting I'll report here.