NOTE: excellent review.
Can you please explain in detail the steps, and also from where to get the U1 firmware?
Am also on AT&T.
Download Firmware N960U1 (in this case N960U1UEU1ARJ5) you can use SamFirm 0.3.6 with this values: Model SM-N960U1, Reg...
Connect Mate as FastBoot
Install TWRP Recovery
Now we have to do a "Wipe Advenced"
Wipe> Wipe Advanced> System ('system' only)
After "Format Data"
Wipe> Format Data, confirm with "yes"
With this, we recover from these errors: ...