Mosquitto inactive but no errors?

i have a weird problem with my mqtt setup. I switched from zha to zigbee2mqtt a few days ago. Everything was fine. Integrated a couple of devices and all worked as intended.
BUT: a few hours later my mqtt devices are all not reachable. The weird part is, in zigbee2mqtt everything is there and can be controlled. i get no errors from mosquitto.
if i restart mosquitto, zigbee2mqtt alarms me about no mqtt available until its up again.

i tried connecting with mqtt explorer. connecting works, but nothings there

anyone get any ideas where to look to find a solution or at least how to find the problem?

ps: tried reinstalling mosquitto

System: rpi3b, hassos