[Q] Stuck in Bootloader/Fastboot, can't access or flash recovery, RUU failed, help? topic

So last week I reverted back to stock recovery to get the OTA 4.4.4 update. That went fine, so last night I tried to install a custom recovery again... which I'm not sure was actually successful, but basically, the phone is now stuck in hboot/fastboot. Attempting to reboot into recovery just reboots the phone into fastboot.

I unlocked and did S-off last year. Had a recovery (not sure which, I think twrp) but was still on stock rom. Interestingly, the banner at the top used to say the software was modified, but ever since I got this problem it now reads "software status: official". Also, the value for both the "radio" and "OpenDSP" fields on the fastboot screen is "INVALID_VER_INFO", which I don't know is pertinent or not but I don't think it was like that before.

I did a ton of research and I found this unresolved thread which seems to have the exact same situation. To be specific, "adb devices" command doesn't show any devices, "fastboot devices" shows the device, multiple attempts at flashing different recoveries via fastboot fail, running an RUU exe from windows fails (error [170]: USB CONNECTION ERROR), running a bootable RUU from extSD card fails (after it asks me if I want to update, and I select yes, it then returns a "partition update failed" error).

I'm seriously stumped and I'm not sure what else I can do at this point. Any advice or help?

getvar all dump:
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0000
(bootloader) version-baseband: INVALID_VER_INFO
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 3.42.502.1
(bootloader) version-misc: PVT SHIP S-OFF
(bootloader) serialno: xxxxxxx
(bootloader) imei: xxxxxxxx
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul_ca
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B12000
(bootloader) cidnum: CWS__001
(bootloader) battery-status: good
(bootloader) battery-voltage: 0mV
(bootloader) partition-layout: Generic
(bootloader) security: off
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: 56f9ae32
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0