I'm waiting on my replacement device so I'll be watching to see how it goes for you. Good luck!
I should probably post this in the T-Mobile forum.
I used PrinceComsy Odin and flash passed with no problems.
Phone booted up and setup fine. No T-Mobile apps or anything and no T-Mobile splash screen.
Model shows as G955W now.
Inserted and non-T-mobile sim and got a 'SIM not supported pop up'. Not a prompt for unlock code.
Was able to access APN and could add an APN but would not save. Hit Save and just went to previous screen without saving.
No service with non-T-Mobile sim so appears still locked.
Was trying this to see if I would get an unlock code prompt and maybe have a way to unlock T-Mobile models without the unlocking App.