I see the problem in openssh-server.postinst. When only a non-default Port is used (and ListenAddress is left alone), the temporary addresses.conf.new file is never moved to it's final location. So, when the ListenStream=<port> line is appended to the final file, the '[Socket] ...' portion is not there.
I see the problem in openssh- server. postinst. When only a non-default Port is used (and ListenAddress is left alone), the temporary addresses.conf.new file is never moved to it's final location. So, when the ListenStream=<port> line is appended to the final file, the '[Socket] ...' portion is not there.