v12.6 to v13.1 Mysql access issue

Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes

Describe the bug

After doing 3+ intances of this same upgrade without issue I did this last one by doing a docker upgrade as well (from v28.2.2 to v28.5.2).

Regardless, when starting up after a fresh upgrade I get this repeatedly:

[11/9/2025] [12:04:48 AM] [Global   ] › ✖  error     Startup Error: Access denied for user 'nginxProxyManagerUser'@'nginx-proxy-manager.hosted06_default' (using password: YES) Error: Access denied for user 'nginxProxyManagerUser'@'nginx-proxy-manager.hosted06_default' (using password: YES)
    at Packet.asError (/app/node_modules/mysql2/lib/packets/packet.js:740:17)
    at ClientHandshake.execute (/app/node_modules/mysql2/lib/commands/command.js:29:26)
    at Connection.handlePacket (/app/node_modules/mysql2/lib/base/connection.js:477:34)
    at PacketParser.onPacket (/app/node_modules/mysql2/lib/base/connection.js:93:12)
    at PacketParser.executeStart (/app/node_modules/mysql2/lib/packet_parser.js:75:16)
    at Socket.<anonymous> (/app/node_modules/mysql2/lib/base/connection.js:100:25)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at Readable.push (node:internal/streams/readable:392:5) {
  code: 'ER_ACCESS_DENIED_ERROR',
  errno: 1045,
  sqlState: '28000',
  sqlMessage: "Access denied for user 'nginxProxyManagerUser'@'nginx-proxy-manager.hosted06_default' (using password: YES)",
  sql: undefined
}

Relevant section of my compose file:

  nginx-proxy-manager:
    container_name: nginx-proxy-manager
    image: jc21/nginx-proxy-manager:latest
    restart: unless-stopped
    environment:
      - TZ=Europe/London
      - PUID=1007
      - PGID=1007
      - DB_MYSQL_HOST=mariadb
      - DB_MYSQL_PORT=3306
      - DB_MYSQL_USER=nginxProxyManagerUser
      - DB_MYSQL_PASSWORD=nginxProxyManagerPassword
      - DB_MYSQL_NAME=nginx_proxy_manager
      - DISABLE_IPV6=true
    ports:
      - 80:80
      - 443:443
      - 127.0.0.1:82:81
    volumes:
      # Make sure this config.json file exists as per instructions above:
      - /docker/nginx-proxy-manager/config/config.json:/app/config/production.json
      - /docker/nginx-proxy-manager/config:/config # only for files.htaccess for now but why not
      - /docker/nginx-proxy-manager/data:/data
      - /docker/nginx-proxy-manager/letsencrypt:/etc/letsencrypt
    depends_on:
      - mariadb

  mariadb:
    container_name: mariadb
    image: lscr.io/linuxserver/mariadb:latest
    restart: unless-stopped
    environment:
      - TZ=Europe/London
      - NOTUSED_MYSQL_ROOT_PASSWORD=npm
      - NOTUSED_MYSQL_DATABASE=npm
      - NOTUSED_MYSQL_USER=npm
      - NOTUSED_MYSQL_PASSWORD=npm
    volumes:
      - /docker/mariadb/config:/config
    ports:
      - 127.0.0.1:3306:3306

Nginx Proxy Manager Version

v13.1

To Reproduce

I installed a mysql client on the nginx-proxy-manager container and can access things ok:

[root@docker-76707f145fa1:/app]# mysql -h $DB_MYSQL_HOST -u $DB_MYSQL_USER -p$DB_MYSQL_PASSWORD -D $DB_MYSQL_NAME
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 1208
Server version: 10.11.6-MariaDB-log Alpine Linux

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [nginx_proxy_manager]> show tables;
+-------------------------------+
| Tables_in_nginx_proxy_manager |
+-------------------------------+
| access_list                   |
| access_list_auth              |
| access_list_client            |
| audit_log                     |
| auth                          |
| certificate                   |
| dead_host                     |
| migrations                    |
| migrations_lock               |
| proxy_host                    |
| redirection_host              |
| setting                       |
| stream                        |
| user                          |
| user_permission               |
+-------------------------------+
15 rows in set (0.003 sec)

MariaDB [nginx_proxy_manager]> quit
Bye
[root@docker-76707f145fa1:/app]# echo $DB_MYSQL_NAME 
nginx_proxy_manager

However found it curious that the container stdout logs show $DB_MYSQL_NAME.$HOSTNAME_default (which is the default docker network name), so tried this and it fails - unsure where it might matter within nginx-proxy-manager though:

[root@docker-76707f145fa1:/app]# mysql -h $DB_MYSQL_HOST -u $DB_MYSQL_USER -p$DB_MYSQL_PASSWORD -D $DB_MYSQL_NAME.hosted06_default
ERROR 1044 (42000): Access denied for user 'nginxProxyManagerUser'@'%' to database 'nginx_proxy_manager.hosted06_default'

As this is my last instance I'm sure it's just the docker upgrade that might have broken it, however I'm still confused where the $HOSTNAME is being picked up and where it is used within nginx-proxy-manager in the configuration above so I can get things up and working again.

Expected behavior

No database errors

Start with the startup database connection path shown by the mysql2 stack trace and compare its DB_MYSQL_* environment variables with the provided Docker Compose configuration. Reproduce the connection using the mysql client and inspect the container logs, then verify that the application starts without ER_ACCESS_DENIED_ERROR while using the intended database and user.