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I think your answer resides in the OP, though I'm not too familiar with AOSP roms, I do know that a lot of updates have hit, and the firmware registers with the towers.
Likely have to update on TouchWiz to the latest.
Perhaps someone else that uses those roms can chime in.
Sent from my SM-N900P using Xparent BlueTapatalk 2
This thread should give you a starting-point. You may also try the AOSP threads. Remember, this is a starting point; I have no idea what base you were on prior to flashing your AOSP rom (MJ4, NAB, NC5), but this was someone using AOSP CM11 and started with MJ4. Please tread with caution.