Default exception handler when connecting to Moodle with authloginviaemail activated

Multiple Moodle platforms, same version of Moodle (3.4.2+ Build: 20180322), the one with authloginviaemail enabled can't be joined by mobile app (codingerror) while the one for which it is not activated works fine.

Context is :

• Android Mobile App (tested on Android 8.1 system)
• Error message is :

Default exception handler: Erreur de programmation détectée. Ceci doit être corrigé par un programmeur : Invalid json in request: Syntax error
Debug:
Error code: codingerror
line 42 of /lib/ajax/service.php: coding_exception thrown