App detects proxy


today I was interested to lookup the traffic of an app.
Actually everything worked like it should, except that the main functions are kind of “blocked”, when I try to use them in the app. But when I leaf the proxy e.g. turn off my wifi, the app works like it should.

At work we are using a proxy too, but the app works there without problems.
How can the app detect the mitmproxy and is there a way to get around it?

Which mode are you using? Regular or transparent? Proxy is often dected by apps.