Several years later this undocumented anti-feature is now fixed:
Repo: GitHub - bkerler/edl: Inofficial Qualcomm Firehose / Sahara / Streaming / Diag Tools :)
Readme: edl/sierrakeygen_README.md at master · bkerler/edl · GitHub
AT!OPENLOCK?
81F2B4F0A9E06DF2
OK
AT!OPENLOCK="21A68A014A39E0E8"
OK
AT!PCFCCAUTH=0
OK
AT!PCFCCAUTH?
NV Setting: 0
FCC Auth Enabled: 1
FCC Lock State: 1
OK
AT!PCFCCAUTH=0
OK
AT!RESET
OK
at!entercnd="A710"
OK
AT!PCFCCAUTH?
NV Setting: 0
FCC Auth Enabled: 0
FCC Lock State: 0