Hello,
I suggest contacting Support about this issue so they will know about it.
Do include screenshots and a detailed explaination (Example - When does the gameflip app log out for you? Is it when you close the app etc.) because there are a lot of different factors that could possibly lead to this.
https://gameflip.zendesk.com/hc/en-us/requests/new
Closest Reference - App sign out Android.
Not Apple but it did happen before to others.
I use andriod currently and there seems to be no issue for me.
Goodluck.