ZTE Z222 Direct Unlock Failed Due to “Unknown Firmware”

I need to report the failure of "Direct unlock" for ZTE Z222. Previously, I have unlocked over 100 units without any problem. However, there is a unit with firmware "ATT_AM_P671B41V1_0_0B16-S" dated Sep, 2015, pops up a question if to use the heuristic method. I tried, nothing works.

BTW, I just downloaded the newly released 2.15.01 software and it is not working with the new ZTE firmware version.

Please help on this issue. Thanks! Let me know how to help.