[Fire TV Q&A, Help & Troubleshooting] Pachacouti:
I did read the unbrick thread, but it's rather old now, and I'm sure a few things have changed since 2019, and 6 amazon updates later... I just watched kamakiri do it's stuff, paid attention to what it flashed, df'd for the partitions, wiped all the partitions I could find in my attempts to get out of the blackscreen, all failed. I knew Tz was flashed to tee1, and I know tee2 is half filled with tee1, it's kind of like the wpa pin to me, the first four digits are the actual pin, the 2nd 2 are a checksum of the first 4, and the last two are a checksum of the first 4 + the 1st checksum, and I'm betting this is what Tee2 is, and KB is the file that says if you can downgrade or not, just a guess, probably completely wrong, but that was my thinking. In the end, it's obvious that a stock image would correct any errors, or flashed partitions, partitions being wiped, and I did make it clear, in the end, I did indeed flash the ORIGIONAL STOCK VERSION, ie, 6.2.6.8 that came with the stick, flashing the boot.img I extracted from the stock firmware, BEFORE flashing the stock firmware.

To sum up as simple as I could:

Load Kamakiri, apply the first step, I wiped the partitions mentioned, meaning before I did the 2nd step in kamakiri, I had wiped boot and system, then I unplugged, I plugged back in, and re-run the first step, which placed fastboot onto firestick, then I rebooted into windows, of course the reboot forced the firestick to reboot, into fastmode, since it could go no further. In windows, I flashed boot.img and twrp. I then rebooted the firestick into twrp, and did the stock flash, rebooted firestick, voila. Stock downgrade complete, and working, after deleting the partitions mentioned.

As I saw it, I could delete anything that would be reloaded by kamakiri, each time it is ran, and this turned out to be correct. In particular, I had tried so many times, that I know I formatted EVERY partition showing in kamakiri terminal, that could be wiped. I noticed kb could not be wiped, but it could be formatted by using the command

fastoot format '' <-Thats 2 ' , not the " used in quotes.

Now if kb is generated from Tee1 & Tee2, and the three were wiped, then I did the 1st kamakiri step, then surely Tee1, Tee2, and kb would be corrected to it's origional written by the kamakiri process.

Now since I got back in, I've decided not to flash magisk for now, diasbled adb when not using it, since I can run stbemu without root, and for the first time I see attempts to log into my secondary router that I use for my firestick due to it's inability to login to hidden wifi, these logs were generated starting from 23:33:23.pm at night, just after I switched off ps4 to go to sleep. Now what script kiddie starts hacking at exactly 23:33:23? Right when I plugged in firestick, big tech on their daily kick routine, trying to kill the firestick. Note the bad password attempts made via gui, ie, they tried to log in to my tomato web gui, and I know it was them, because at 5.11am, I was watching john wick on the firestick, and I saw a strange thing. My firestick appeared to die again, including no pic on tv, swiss tv, (snow style screen) and a split second later there was john wick kickin ass. I'm betting if I had adb enabled, the firestick would be dead again. So to prevent amazon doin jack **** to kill your stick, disable adb when not using it.

Ps, I obviously know my tomato routers password, at no time was anything else connected to this router. Remember, if you got root, and leave adb enabled, then so have they.

Jan 29 23:33:23 StudioFire daemon.warn httpd[2987]: Bad password attempt (GUI)

Jan 29 23:33:25 StudioFire daemon.warn httpd[2992]: Bad password attempt (GUI)

Jan 29 23:59:00 StudioFire cron.info crond[971]: USER root pid 4017 cmd /usr/sbin/webmon_bkp hourly

Jan 30 00:00:00 StudioFire cron.info crond[971]: USER root pid 4072 cmd logger -p syslog.info -- -- MARK --

Jan 30 00:00:00 StudioFire cron.info crond[971]: USER root pid 4073 cmd /usr/sbin/webmon_bkp

Jan 30 00:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 00:00:00 StudioFire user.notice Webmon-Backup: Backup finished.

Jan 30 00:59:00 StudioFire cron.info crond[971]: USER root pid 6478 cmd /usr/sbin/webmon_bkp hourly

Jan 30 01:00:00 StudioFire cron.info crond[971]: USER root pid 6533 cmd logger -p syslog.info -- -- MARK --

Jan 30 01:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 01:59:00 StudioFire cron.info crond[971]: USER root pid 8891 cmd /usr/sbin/webmon_bkp hourly

Jan 30 02:00:00 StudioFire cron.info crond[971]: USER root pid 8946 cmd logger -p syslog.info -- -- MARK --

Jan 30 02:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 02:59:00 StudioFire cron.info crond[971]: USER root pid 11304 cmd /usr/sbin/webmon_bkp hourly

Jan 30 03:00:00 StudioFire cron.info crond[971]: USER root pid 11359 cmd logger -p syslog.info -- -- MARK --

Jan 30 03:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 03:59:00 StudioFire cron.info crond[971]: USER root pid 13717 cmd /usr/sbin/webmon_bkp hourly

Jan 30 04:00:00 StudioFire cron.info crond[971]: USER root pid 13772 cmd logger -p syslog.info -- -- MARK --

Jan 30 04:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 04:59:00 StudioFire cron.info crond[971]: USER root pid 16130 cmd /usr/sbin/webmon_bkp hourly

Jan 30 05:00:00 StudioFire cron.info crond[971]: USER root pid 16185 cmd logger -p syslog.info -- -- MARK --

Jan 30 05:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 05:11:33 StudioFire daemon.warn httpd[16649]: Bad password attempt (GUI)

Jan 30 05:59:00 StudioFire cron.info crond[971]: USER root pid 18758 cmd /usr/sbin/webmon_bkp hourly

Jan 30 06:00:00 StudioFire cron.info crond[971]: USER root pid 18813 cmd logger -p syslog.info -- -- MARK --

Jan 30 06:00:00 StudioFire syslog.info root: -- MARK --

Jan 30 06:48:06 StudioFire daemon.warn httpd[20737]: Bad password attempt (GUI)

Jan 30 06:59:00 StudioFire cron.info crond[971]: USER root pid 21337 cmd /usr/sbin/webmon_bkp hourly

Jan 30 07:00:00 StudioFire cron.info crond[971]: USER root pid 21392 cmd logger -p syslog.info -- -- MARK --

Jan 30 07:00:00 StudioFire syslog.info root: -- MARK --

So I say to those who log their stuff, when the firestick goes down, check your router logs.