Just a FYI...
[root@test configs]# docker-compose up -d plex
Removing plex
Recreating e93fdee716_plex
[root@test configs]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
6fe3cc058991 plexinc/pms-docker "/init" 10 seconds ago Up 10 seconds plex
[root@test configs]# docker logs -f plex
[s6-init] making user provided files available at /var/run/s6/etc...exited 0.
[s6-init] ensuring user provided files have correct perms...exited 0.
[fix-attrs.d] applying ownership & permissions fixes...
[fix-attrs.d] done.
[cont-init.d] executing container initialization scripts...
[cont-init.d] 40-plex-first-run: executing...
Creating pref shell
Attempting to obtain server token from claim token
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1 0 1 0 0 2 0 --:--:-- --:--:-- --:--:-- 2
Plex Media Server first run setup complete
[cont-init.d] 40-plex-first-run: exited 0.
[cont-init.d] 50-plex-update: executing...
[cont-init.d] 50-plex-update: exited 0.
[cont-init.d] done.
[services.d] starting services
[services.d] done.
Starting Plex Media Server.
And I have a web page I can login to (though I have this on cloud box and doing over a VPN - need to probably open up some ports now)
So it seems that at least at the minute it works