App rejected due to no response when clicked on Log in button.

We are building a B2B app and recently we have submitted it for the review. We got replies saying that the app is not giving any response when clicked on login button after providing the given credentials. We did get some other suggestions and advises regarding other features. Anyways about login we tested the same build on the same device and iOS version and it is working. In the process I even bought two iPhones and an iPad. It’s working alright on all of those. We even tested the same build on iPhones/IPads that are outside of our organization through Test Flight just to make sure and it’s working. Is there anything we are missing? Frame work used: Flutter Login works through Firebase Authentication Tested on IPhone 12, 13, 13 pro max with iOS 15.0, 15.2 and also on iPhone 8 model with Older iOS version also on IPad Pro 12.9 with iOS 15.2 (This is what Apple has been testing on). Thank you