Flutter application not working correctly with burp proxy

Question

I have a Flutter application. I have to perform a penetration test on it. I used proxydroid to intercept requests since normal proxy settings don't work with this app. I successfully see the requests on burp, and receive a response from the server. However as soon as the response is sent to the application, a generic error message appears. I already thought about a parsing error. Without burp or with tls passthrough the app works perfectly. How can I understand what may cause the problem? I also tried to change iptables settings and set up invisible proxy on burp settings. The behaviour of the app is still the same. Is there something about flutter that understands that I use a proxy and stops the application from working properly? technically the application is set up by the developers to facilitate penetration tests so I don't expect any additional controls.