Response Header from /subfolder are wrong or missing

[Jackson085]

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
I would like to achieve the following:
http://dev.local/ -> http://192.168.178.181:81
http://dev.local/app -> http://192.168.178.181:5000

But when I go to http://dev.local/app, I can see in the dev tools that it is trying to load the .js and .css files as text/html content

When i map http://dev.local/ -> http://192.168.178.181:5000 the page loads and the content type is set correctly

Nginx Proxy Manager Version
v2.11.1

Additional context
When I initially started with custom locations, I received this Problem (Error after updating - map not allowed here) so I used this workaround #3474 (comment)

[Jackson085]

I finally found the bug. The index.html was loaded correctly but not the .js and .css files.

How did I "fixed" it?
I added a base tag to the index.html
<base href="/app/">