[Help] Can't flash system images to xt1031 Republic Wireless topic

So, last week I received the update to 4.4.4 on my Republic Wireless xt1031 (locked bootloader), then quickly realized that I preferred 4.4.2. After this, I downloaded the official republic wireless 4.4.2 firmware and attempted to flash it with fastboot, which didnt do anything but wipe my data. I then retried with mfastboot, which softbricked my phone. Whenever I try to flash any of the many stock firmwares I have found (tried Republic Wireless, Boost and a couple other firmwares, including a couple 4.4.4 firmwares), it seems that everything has been able to flash over and is working other than the system image files (system.img_sparsechunk1, system.img_sparsechunk2, system.img_sparsechunk3 for the stock republic wireless firmwares). Whenever I try to flash any of the 3 over, I get an error on the phone:

hab check failed for system
Invalid PIV signed system image

and in my command prompt:

...\falcon_repw_user_4.4.2_KXB20.9-1.10-2.27_33_release-key
s-cid6.xml>mfastboot flash system system.img_sparsechunk1
target max-sparse-size: 256MB
sending 'system' (256840 KB)...
OKAY [ 8.056s]
writing 'system'...
(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)
finished. total time: 8.464s

I've heard this can be an issue with a locked bootloader, but I've also read that people can flash stock roms with a locked bootloader as long as the firmware is specifically for your phone. Does anyone have any advice on this issue? I'm just about at my wit's end here. I have tried at least 6 different firmware, I've intentionally hardbricked it by destroying the bootloader, then reflashed it with blankflash and Motoflasher on two separate tries and still no luck. Currently, it goes through the boot process but just boots to a black screen. Any help would be greatly appreciated.