Ubuntu is blocking all outside connection

I've got this problem where I lose all means to connect to my server from time to time. Today I finally managed to pinpoint the exact moment when it happened, and found what I think is the journalctl entry related to my problem. Now I don't know what to do with it. It does seem kind of concerning. The logs are as follows: Aug 21 12:34:49 woegoef systemd-networkd[921]: br-69b2ffc9017a: Gained…