thank you eps!
that app is a student notebook. it does not use wifi. it only work with local data ( a sqlite database). it's installed in the internal sd card and also the database. it has a file ( text file) that is used to tell in what directory the database is and where also is the students photo directory. it also has a keystore file (ver 2) where i have some parameters like student absence code and others ( to make more simple to register those events) and that's all . As i've said, it worked yesterday with no problems!
the os (android v7) has not been update since yesterday. the only automatic update was google play services for instant apps .
Thank you!