I tested it just updating my old docker, only editing the Repository to registry.gitlab.com/bockiii/deemix-docker and clicked Apply.
It updated, and is running now. It took a couple of stops and starts though because notabug.org, where deemix-webui is hosted, is currently under a DDoS attack.
If you get this message in the logs, then it's most likely because of the DDoS attack:
[cont-init.d] First start, cloning repo
Cloning into 'deemix'...
fatal: unable to access 'https://notabug.org/RemixDev/deemix-pyweb.git/': The requested URL returned error: 504
When it starts up correctly, it's normal to see this in the log (at least, for me it is normal, it runs and I can access it:):
Starting server at http://0.0.0.0:9666
* Serving Flask app "server" (lazy loading)
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off