Problems with different S7 models and GearVR apps anyone?

I have a GearVR app. It is sideloaded with corresponding Oculus ID and works fine on my European phones (6x S7 model “SM-G930F”).
My customer in Canada don’t get it to work on his 3x S7 “SM-G930T” models. The “T” seams to indicate this are “t-mobile” branded phones.
Their DeviceIDs are strangely short (8 characters instead of my phone’s 18 chars) but seams legit, we don’t get “APK not signed errors”. Instead the app crashes to black after a few seconds.
Does anybody know this behavior?

you might want to ask that Oculus directly, on their forums.