MongoDB in android, dont keep data after lauch app

I made a little app, with insertion of data in a collection with mongoDB, it works fine over my PC, but over android in my smartphone,… the data dont persist after re lauch app. ¿why?

and other error, the type Date d = new Date(), is always null over the smartphone. ¿why?

¿¿¿ I need a credentials, permission, privileges, ???’