Hi Mohamed, this might happen because the session becomes invalid. Try changing the session timeout paramater in the custom settings of the runtime configuration, see https://docs.mendix.com/refguide6/custom-settings#1-custom-settings
And for mobile you could also use this widget: https://appstore.home.mendix.com/link/app/108446/Magnus-Consulting/InsomniaForPhoneGap-
Regards,
Ronald