sorry to say but I did a very stupid thing. 
We do have a docker-compose installation of nextcloud 14.0.3 running on Ubuntu 16.04.5 LTS that was running fine.
But I just did docker-compose pull then docker-compose build, docker-compose stop and docker-compose up -d
Now I do only see a white page when accessing the nextcloud URL.
docker-compose ps does show that the db is always restarting.
And looking at the db log it does show the error:
db_1 | 2018-11-06 18:27:46.924 UTC [1] FATAL: database files are incompatible with server
db_1 | 2018-11-06 18:27:46.924 UTC [1] DETAIL: The data directory was initialized by PostgreSQL version 10, which is not compatible with this version 11.0 (Debian 11.0-1.pgdg90+2).
Somehow the database now seem to be on version 11 but the directory is for version 10.
What can I do to solve this problem?
Is there a way to go back to version 10 or is there a way to migrate the directory to version 11?
best regards
Guido