Thanks for the advice that I have to forward /x only. Now my proxy config looks as you explained in this thread: Webinterface difficulties
Now when I access the web interface via the reverse proxy I am presented the unrendered html page and given the following errors:
Firefox console:
"The character encoding of the plain text document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the file needs to be declared in the transfer protocol or file needs to use a byte order mark as an encoding signature."
Chrome console:
"Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self' https://maxcdn.bootstrapcdn.com". Either the 'unsafe-inline' keyword, a hash ('sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ='), or a nonce ('nonce-...') is required to enable inline execution."