I also have an iPhone 7 and the login screen just sits there...wont let me enter my password. I tried:
1 - Force quite the app
2 - Restarted the iPhone
Nothing works. I left a NASTY column of feedback on DJI's app review. This is seriously ridiculous. I will try to delete and reinstall the app next...but I don't think that will help. Anyone hear anything on this?