We had an UniFi controller installation where we were unable to adopt a small amount of devices, like three out of forty. It was very strange, everything worked perfecly except those few.
The error we found in /var/log/unifi/server.log was just:
server.log:[2019-06-20T16:11:53,707] INFO dev - [state] dev[aa:aa:aa:aa:aa:aa] UNKNOWN->INFORM_ERROR, state_expire=0
We tried manually updating the firmware of the switch via ssh, but there was just a minor version upgrade and it changed nothing.
Then I found an old thread on UniFi forums saying they solved a similar error by setting a manual IP for the hostname unifi in /etc/hosts. This looked a little weird to me because we were trying to inform using an IP address, but we tried everything so was worth a try.
So I added
in /etc/hosts, ran
At first on the controller I was still seeing Inform error, but after the second try I finally had Adopt required! Gotcha!
Can’t really tell why, but the /etc/hosts trick did it!