In some devices the credentials are not stored, they need to be entered everytime the app is started. All the cases we detected were with Samsung Galaxy S4 Mini.

Forum post:

https://moodle.org/mod/forum/discuss.php?d=318435

Thanks to that test we discovered that, for some reason, in that device the IDBObjectStore.count() function is not implemented. Maybe there are some other functions not implemented, who knows.

One possible solution is to check if that function exists and, if it doesn't, force to use WebSQL.