Samsung Tab S2 'Power Off' then DEAD - weird! - Android Q&A, Help & Troubleshooting

So, after having two amazing Tab S (first one) and not being able to find a third, I ended up "upgrading" to a Tab S2. (Less screen resolution didn't seem like an upgrade..but hey)
After using it for about a year or so, I finally decided to get off my ass and root it. Had no problems after rooting it. Life was great. Maybe 6-7 months after rooting it, one day it booted up with an FRP lock; I didn't reset it at all so..odd..
Put the tablet aside as I didn't really have time to fix it. Few months later, I decide to pull it out wanting to use it for a project (I'm developing WebUSB FTDI drivers which also worth with Android OTG to allow a web page to access a USB device), I never replaced the original recovery, so my options were limited. I was hoping that perhaps flashing a new ROM that I might be able to keep my files versus just doing a reset in the recovery, which I'm not sure would have worked anyway (FRP) (I'm sure I've seen a device where this worked, IE, any user files were stored actually on a separate partition, thus you'd lose your apps and everything but downloads and such on the internal would be kept). I mean, I figured the chances were low but at least hire than the wipe option - not a huge deal anyway, important stuff is on the uSD.
So, I head over to Samsung's site and download the closest looking S2 rom, it's a SM-T713 (Canada, Gold/32GB/WiFi Only).. The ROM I ended up getting happened to have 4G support, so I didn't get a WiFi only ROM like I should have. Flashed it up with ODIN (AP), didn't change/flash the BL at all.
After flash, tablet booted up fine. It mentioned I would have to log in to google to authorize it (FRP lock) - no big deal, although I'm sure I didn't remote lock it. Do my login, finish the setup. Home screen. Tablet is running fine, nice and snappy.
Installed a few apps, it ran for a few days fine, then I decided I should probably flash it again with a WiFi only ROM, so I hold the power button and get the pop up to shutdown / restart, I press 'Power Off', tablet does it's shut down and powers off.
That's it. Now she's dead. Absolutely no sign of life since then. I tried to power it back on immediately as I had planned on going into DFU and plugging it in to upload another ROM. Nothing. No response. Battery was at 50% when I powered off. No battery symbol or anything when plugged in.
I should not that this was not the tablet's first boot since the flash either; it boot looped due to low battery after flashing a few times (damn samsung low battery boot loops) until I got the power supply plugged in, it was the first time that the "Power Off" option was selected, perhaps it hadn't been reset that way too; something on shutdown change something? I mean WTH?
I have tried:
- literally all key combinations for over a minute (PWR + VOL UP, PWR + VOL DWN, PWR + VOL UP + HOME, PWR + VOL DWN + HOME, PWR + HOME, PWR + VOL UP + VOL DWN, PWR + VOL UP + VOL DOWN + HOME) including while plugging it in, unplugging it
- different chargers, cables (bought brand new one), etc.
- left tablet for 2-3 days hoping it would die
- disassembled tablet, remove battery for few hours, replug battery
I have a USB power meter, when I plug in the tablet, it shows that it's pulling 0.57a constantly. I left it on overnight and it was no longer pulling current, just occasionally going from 0.00a to 0.07-0.10a. When plugged in without the battery, it also occasionally goes from 0.00a to 0.07-0.09a or so. Current usage profile is the same without the OLED plugged in. Something inside is at least slightly functioning.
No components that I notice are getting hot or anything obvious.
It was a gift, thus supposedly refurbished. The device looked great when I got it, no scratches or dings or anything, basically brand new looking so I assumed it had been a return, but upon disassembly, I found evidence that the tablet had been disassembled before, there was two-sided tape holding the screen on instead of any proper adhesive; was such a pain in the ass to take apart and not realizing that this was the case until I opened it only made it harder; regardless I doubt that any prior work could've caused this issue.
Does anyone have any schematics for this device or experienced something like this? I have meters, scope, logic analyzer, etc as I already do a bit of hardware reverse engineering and development.
The only thing I can think is somehow the boot loader got fried? Somehow the modem fw got flashed to boot loader? Is that even possible? I'm really reaching here as I'm really not sure, it's odd how it was working fine, had booted several times yet pressing 'Power Off' killed it when it was working fine. I would like to save this device from the graveyard as it's in great condition otherwise. It did sit for quite a while, so I was worried about the battery but plugging it in after sitting I immediately got the charge screen and it charged right up (even though it was still FRP locked at that point of course).
:crying::crying::crying::crying::crying:

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le bump