MQTT not working after migrating HA VM form HyperV to Proxmox


a few days back I migrated my VMs form HyperV to Proxmox. I’ve got all of them working but HA. It does boot just fine and controlling smart home devices works. However entities that work with MQTT like a thermometer and co2 sensor don’t update anymore. Also mqtt nodes used in Node Red are unable to build a connection to the broker.

I’ve checked the Mosquitto broker settings but couldn’t find anything that seems relevant.

I can load a backup I took before the migration and there MQTT works fine however as soon as I reboot the VM it breaks. The output of “ip a show”/“ifconfig -a” are the same and do not change after restoring the backup. The only difference I could make out is MQTT working, temporarily.

Since I wasn’t able to fix this I choose to create a new, clean HA VM and import the backup there, hoping it would stay working after a reboot but this failed as well.

Is this by any chance a known and fixable problem?