Video calling App backed Code error fix

I’m make a Rondom video calling App But Some Times Later App Login Problem, App Crashes Problem and I think Bugs Problem So Can you Solve it It’s just backend Codes in. (Java) language

Problem Activity Info
1:- Login Activity (Direct Google Login System)
2:- Main Activity (After 2-3 Second Automatic App Close )
3:- Others Activity I’m not Opened but you most check Bug and error