Sadly, what most likely happened, is a deleted/faulty SBL partition, this is the Qualcomm bootloader damaged, and only repairable by Qualcomm tools. The device boots to this mode when normal bootloader partition is damaged, thus the device can't boot.
So far none has figured out how to repair this, outside factory (except on XDA forum, for a few devices).
This happened for at least one user here, on J1 (search my answers)