[Shield Tablet Q&A, Help & Troubleshooting] grivad:
This is a strange one for me. Stumped. Been working on it all night, no improvement. New one for me, long-ish description (with detail), but a TL;DR too.

Last night I applied the 1.3 OTA for the K1. Being my K1 was rooted, I followed the process I have always followed by restoring the system images to stock, applying the OTA via recovery, then re-rooting. Process:

Shutdown tablet

Swap married/paired SD card with temp SD containing flashables (OTA, SuperSU)

Boot to bootloader, fastboot (re)flash tablet's current system images (recovery was already stock but flashed again for good measure, boot, system, blob -> staging)

Boot to custom recovery using fastboot boot -recovery image-

Flash OTA from temp SD, wipe caches, apply SuperSU

Shutdown, replace married SD, boot, enjoy life

This time I didn't immediately apply SuperSU, as I thought I'd flash 1.3 and let it go fully stock a bit to ensure no other updates were pending (nVidia seems to like incremental updates, so flashing to 1.1 won't give you an OTA to 1.3 directly, but to 1.2 first, then 1.3). I've also followed this process with the K1 for every update since 1.1 without a hitch, and although there haven't been many OTAs, it has still worked perfectly every time. Because of this and because I've done this a billion times on a million different devices with zero issues ever, I didn't take a backup before the update. Woe is me.

When I rebooted this time after flashing the OTA (no root), it booted up seemingly fine to the "Android is upgrading" modal, so I left the tablet alone for a bit to let it do its thing. When I came back, the tablet was HOT, was at a completely black screen save for the status bar (no wallpaper/launcher besides the clock/wifi icon which showed a connection, that's it). I tried to interact with it and couldn't (totally locked up, also a first), then it rebooted on its own. Subsequent times, during troubleshooting, I noticed that it's totally locked -- NOTHING responds, unless you can get to it before it reboots and hold power to kill it.

First thought was a bad flash. NBD, so went back and reflashed, double-checking everything and carefully following the same process. No dice. I did use a newer TWRP recovery from April of this year initially, which was a recommended version for the K1 specifically, rather than a really buggy but working one from last year. To test I did I try using the older TWRP on one of the next flashes thinking maybe the new one borked the partitions, or at least wasn't writing the partitions/symlinks properly (and the older one was the TWRP I had used for previous updates, with no issues). But, no change..

It took me a long time and many reflashes and cache formatting and digging before I realized if I pulled the married SD out, it booted just fine. Weird, and gets weirder. After leaving the married SD out and booting, and having the tablet working just as expected (except for missing the SD), Android shows a notification saying to reinsert the married SD. Once the married SD is reinserted, things seem OK for a few seconds before the whole system goes unresponsive again, heats up, and begins bootlooping. Before it sh'ts the bed, the message on the status notification asking to reinsert the married SD card doesn't change, but in the Storage settings, it shows it's "checking" the card, followed by a sudden hot death spiral into non-function. If you select the SD from Storage settings to take a look around its contents, the tablet basically locks up instantly. Inserting other SDs works fine (for the most part, still some other weirdness), it's just the married SD that totally kills the device without fail.

Obviously I'd like to avoid wiping and reinstalling the whole thing if it can be avoided, not just because my dumb ass didn't take a backup so I'd lose a ton of app/game data, but also because it's a just huge pain. A lot of the sites that offered "fixes" for these types of problems say to just wipe data, which is not a solution and is the nuclear option (like telling someone to to replace a car due to a flat tire).

Ideas? Is this as simple as recreating some symlinks that somehow disappeared and refuse to come back after all the flashes, and if so, how? I've been looking for hours and haven't found anyone with this particular issue or steps to correct.

[size=+2]TL;DR[/size]: Applied K1 1.3 OTA, married/paired SD card is no longer recognized, causes tablet to hard-lock and enter bootloop when inserted (other SDs do not cause this issue).

Other potentially pertinent bits:

Initial flash was dirty, second and subsequent flashes included a wipe of system first

Installed 1.2 images first, then tried going back to 1.1.1 and taking nVidia's OTAs to get back up to 1.3

1.1.1 does not recognize the married SD but doesn't kill the tablet, while 1.2 and 1.3 kill the tablet when the SD is inserted

When married SD is not inserted, using shell or ES Explorer or otherwise, not seeing a /storage/emulated/0, or /sdcard, or /data/media, or any other familiar storage related directories

When married SD is inserted, it dies too fast to look around much or try to do anything to check/fix the SD itself

/storage is totally empty except for a folder called "self", and inserting a working SD creates a directory under /storage labeled with the SD's serial number (not an emulated/0 directory or anything similar)

Not sure if this is expected behavior since the SD was married -- do those directories/symlinks live on the SD now since it's married, and won't show up in the device filesystem until everything's properly mounted?

Tried following these steps, which although written in the N5 forum, still seemed relevant.. no change

Tried the referenced SD permissions update with the card inserted and not, in case of the directories it touches only being visible/available with the card inserted, no change

Noticed even within TWRP, going to the "mount" menu seemed flaky, labored, and didn't show what I expected, but this could be because there isn't a "proper" or official custom recovery for the K1 yet and things are just buggy

ES File Manager still seems to think an /sdcard directory exists and tries to open to it, and just spins in an open directory.. as expected

Going to /data in ES File Manager shows me an empty directory with a message stating the SD card is missing

Using a working, freshly formatted SD in the tablet and trying to point Titanium to a directory on the SD gives me messages about the directory being unwritable, no matter where I go on the SD

Titanium's app permissions (including r/w storage) are proper, SD is not write protected (freshly formatted on the tablet)

Tried using SDFix, which also gave me an error re: "platform permission file is invalid"

There's probably more I'm missing, but can't remember it all -- I have tried everything, I feel like, and have been at it for 13 hours now (apologies if this is written spotty, fighting to keep my eyes open).

So is it totally hosed, or is this recoverable? Is there a way to fix the tablet to recognize the SD, or fix the SD itself if that's the issue (but I'd wonder how it got corrupted in the first place, since it has only been removed once fully powered down)? Is there at least a way to check the married SD for corruption or issues?

Thoughts?

EDIT: Formatting