WebDAV with Docker Nextcloud

I’m running nextcloud together with nginx, lets encrypt and proxy inside some docker container. Works perfect.
On my last nextcloud installation (native on a system, so there was no docker container at all) i could use WebDAV without any problems but now i cant connect to webdav.

I use the WebDAV link which i get and looks like similar this:
http://mydomain.com/remote.php/dav/files/user/

Some examples: Windows dont know the link and keepass tusk. Keepass tusk give the error:

Error: Invalid response: 500 Internal Server Error

With my old native nextcloud installation, that was not a problem.

Maybe this can help, my docker-compose.yml which i used for this setup:

version: '3'

services:

  proxy:
    image: jwilder/nginx-proxy:alpine
    labels:
      - "com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy=true"
    container_name: nextcloud-proxy
    networks:
      - nextcloud_network
    ports:
      - 80:80
      - 443:443
    volumes:
      - ./proxy/conf.d:/etc/nginx/conf.d:rw
      - ./proxy/vhost.d:/etc/nginx/vhost.d:rw
      - ./proxy/html:/usr/share/nginx/html:rw
      - ./proxy/certs:/etc/nginx/certs:ro
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/tmp/docker.sock:ro
    restart: unless-stopped

  letsencrypt:
    image: jrcs/letsencrypt-nginx-proxy-companion
    container_name: nextcloud-letsencrypt
    depends_on:
      - proxy
    networks:
      - nextcloud_network
    volumes:
      - ./proxy/certs:/etc/nginx/certs:rw
      - ./proxy/vhost.d:/etc/nginx/vhost.d:rw
      - ./proxy/html:/usr/share/nginx/html:rw
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro
    restart: unless-stopped

  db:
    image: mariadb
    container_name: nextcloud-mariadb
    networks:
      - nextcloud_network
    volumes:
      - /srv/docker-persist/MariaDB/nextcloud-sql:/var/lib/mysql
      - /etc/localtime:/etc/localtime:ro
    environment:
      - MYSQL_ROOT_PASSWORD=rootpwd
      - MYSQL_PASSWORD=pwd
      - MYSQL_DATABASE=ncdb
      - MYSQL_USER=nextcloud-dbuser
    restart: unless-stopped

  app:
    image: nextcloud:latest
    container_name: nextcloud-app
    networks:
      - nextcloud_network
    depends_on:
      - letsencrypt
      - proxy
      - db
    volumes:
      - nextcloud:/var/www/html
      - ./app/config:/var/www/html/config
      - ./app/custom_apps:/var/www/html/custom_apps
      - /mnt/NC:/var/www/html/data
      - ./app/themes:/var/www/html/themes
      - /etc/localtime:/etc/localtime:ro
    environment:
      - VIRTUAL_HOST=VIR_HOST
      - LETSENCRYPT_HOST=LE_HOST
      - LETSENCRYPT_EMAIL=MAIL
    restart: unless-stopped

volumes:
  nextcloud:
  db:

networks:
  nextcloud_network:

Problem still exists. Do i have to activate WebDAV? If not, what could cause this issue?

Maybe the problem could be docker? I’ve got an letsencrypt certificate and can reach nextcloud over https online (not only in my local network!).
Like this
https://myserver.com/remote.php/dav/files/user/

but the WebDAV section (also also settings > system) reports
http://myserver.com/remote.php/dav/files/user/
no https at all.

Is this the problem? If yes, how to fix this?

With only http you must configure https (TLS) e.g. with Lets Encrypt.

@devnull see above, i used lets encrypt. I can access the website with https and its a valid certificate. I put this line into my config.php
'overwriteprotocol' => 'https',
and now, the webdav link is like https://myserver.com/remote.php/dav/files/user/.

But what I found out: I can access webdav with my main account, but with another account (seems no different at all, normal username with password) i’ll get the error 500. What could cause this for one account but not for another?