Dear Juan,
I tried again both Moodle instances via mobile app, however I cannot seem to see the additional field "gateway=true" on the website address during the SSO authentication. How did you get this additional field when you login in the mobile app via mygust.gust.edu.kw while the other instance mdltest.gust.edu.kw do not have this additional field? When I try to login on both Moodle instances of ours, I do not see this "gateway=true" additional field.