XT1053 20 sec reboot loop

XT1053 yesterday got into a never-ending reboot loop on around 20th second of loading up. I think the phone had the latest firmware update on it.

I tried to upload a new firmware:

GHOST_RETAIL_5.1_LPA23.12-15_cid9_CFC
RETAIL-US_4.4.4_KXA21.12-L1.29.1_2_cid9_CFC_1FF
TMO_5.1_LPA23.12-15_15

Using RSDLite 6.1.5

I always get:

downgraded security version
update gpt_main version failed
preflash validation failed for GPT

Any ideas how to proceed?

P.S. XT1053 is a US *unlocked* version purchased directly from Motorola.