Ok so I now understand what is happening.
Thanks to this post
Basically because I have a bug when I Deploy on Mobile.
I’m still stuck in version 0.1.0 in Live even though it has been deployed on TestFlight
So then I get the login bug because there is a built-in workflow checking the condition “app_version is app_version” which doesn’t match because it does “0.1.0 not 0.70” (note a/o 14/08 this is incorrect the app version is just going to retrive “test” or “live” not the mobile version)
Good news is now understand what’s going on.
Bad news, is that there is nothing I can do. (or can I ? 
)
Hopefully the support tech team will be able to unstuck me before the end of the mobile challenge.