This issue should only be tested in 1 device. Go to the Moodle database and open the table mdl_config. Edit the setting rememberusername and set some text in it (e.g. "aa"). In web, edit as admin and purge caches. In the app, go to App settings > General and enable "Display debug messages". Try to add the site in the app. Check that in the error modal you see the debug info, something like: "rememberusername => Invalid response value detected ..." Steps 1 and 2 could also be done using config.php file and entering $CFG->rememberusername = 'aa';