I have a pi (old one) which served as MQTT server and a pi 4 as the HA server. Worked for a year, but MQTT pi started failing. Added MQTT on the HA pi, see in the log that devices connect:
1601427261: New client connected from 192.168.136.153 as DVES_D19A74
But the entities seem to keep relating to the old server:
This is not the MQTT broker, this is the Home Assistant MQTT integration, that’s not the same thing. The MQTT integration is used by home assistant to connect to the MQTT broker.