The problem is alpine v3.5 has postgresql version 9.6.1 and the database you have is 9.5
I did this to get it working, just install the 9.5.x version
Probably a way to update the postgresql database but i have not done that. pg_update anyone?
# ssh into your server
# enter musicbrain container
docker exec -it musicbrainz /bin/bash
# then inside the container at the root@87057f3a1aa1:/$
# delete the old postgresql
apk del postgresql
# add the v3.4 repo
echo 'http://dl-cdn.alpinelinux.org/alpine/v3.4/main' >> /etc/apk/repositories
# update
apk update
# install the 9.5.x version
apk add --no-cache postgresql=9.5.6-r0
exit
# restart your musicbrainz docker from webUI
Edit: I still have problems, but not as many. Probably don't follow the guide above.