Docker Nextcloud behind an Apache reverse proxy - Error: OC is not defined etc

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Below is my reverse proxy apache config file

<IfModule mod_ssl.c>
<VirtualHost *:443>
    ServerName        nextcloud.mydomain.com
    ProxyRequests     Off
    ProxyPreserveHost On
    AllowEncodedSlashes NoDecode

    SSLProxyEngine On
    SSLProxyCheckPeerCN on
    SSLProxyCheckPeerExpire on

    <Proxy http://localhost:8015/*>
      Order deny,allow
      Allow from all
    </Proxy>

    ProxyPass         /  http://localhost:8015/ nocanon
    ProxyPassReverse  /  http://localhost:8015/

    Include /etc/letsencrypt/options-ssl-apache.conf
    SSLCertificateFile /etc/letsencrypt/live/nextcloud.mydomain.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/nextcloud.mydomain.com/privkey.pem
</Virtualhost>
</IfModule>

I have Nextcloud/DB running within Docker containers. Here is my docker-compose.yml file:

$ cat docker-compose.yml
version: '2'

volumes:
  nextcloud:
  db:

services:
  db:
    image: mariadb:10.2.33
    command: --transaction-isolation=READ-COMMITTED --binlog-format=ROW
    restart: always
    volumes:
      - db:/var/lib/mysql
    environment:
      - MYSQL_ROOT_PASSWORD=rootpwd
      - MYSQL_PASSWORD=nextcloud
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud

  app:
    image: nextcloud
    ports:
      - 8015:80
    links:
      - db
    volumes:
      - nextcloud:/var/www/html
    restart: always
    environment:
      - OVERWRITEHOST=nextcloud.mydomain.com
      - OVERWRITEPROTOCOL=https

$ docker-compose up -d
Creating volume "nextcloud_nextcloud" with default driver
Creating volume "nextcloud_db" with default driver
Creating nextcloud_db_1 ... done 
                                                                                                                                                               Creating nextcloud_app_1 ... done                  
$ docker ps
CONTAINER ID        IMAGE                           COMMAND                  CREATED             STATUS              PORTS                      NAMES
b208a2e4b391        nextcloud                       "/entrypoint.sh ap..."   21 seconds ago      Up 19 seconds       0.0.0.0:8015->80/tcp       nextcloud_app_1
dfb1b4159212        mariadb:10.2.33                 "docker-entrypoint..."   24 seconds ago      Up 21 seconds       3306/tcp                   nextcloud_db_1
...
5673728a784d        collabora/code                  "/bin/sh -c 'bash ..."   3 months ago        Up 3 months         127.0.0.1:9980->9980/tcp   collabora

But, I’m seeing the following error in my browser console:

Uncaught ReferenceError: $ is not defined
    at (index):34
(anonymous) @ (index):34
nextcloud.mydomain.com/:37 Uncaught ReferenceError: OC is not defined
    at Object.381 ((index):37)
    at r ((index):37)
    at (index):37
    at (index):37
381 @ (index):37
r @ (index):37
(anonymous) @ (index):37
(anonymous) @ (index):37
nextcloud.mydomain.com/:44 Uncaught ReferenceError: OC is not defined
    at (index):44
(anonymous) @ (index):44
nextcloud.mydomain.com/:49 Uncaught ReferenceError: OC is not defined
    at Object.200 ((index):49)
    at t ((index):49)
    at (index):49
    at (index):49
200 @ (index):49
t @ (index):49
(anonymous) @ (index):49
(anonymous) @ (index):49
nextcloud.mydomain.com/:66 Uncaught ReferenceError: OC is not defined
...

By the way, when I run these containers locally (e.g. http://localhost:8015) everything works. So, I’m guessing 1) because I’m behind a proxy and/or 2) HTTP. Any suggestions?