I have the same problem in version 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
$ maas <session> ipaddresses release ip=<ip> force=true discovered=true Unknown alloc_type.
I have the same problem in version 2.2.2-6099- g8751f91- 0ubuntu1~ 16.04.1
$ maas <session> ipaddresses release ip=<ip> force=true discovered=true
Unknown alloc_type.