[T-Mobile Samsung Galaxy S6 Edge] Aou:
Sounds like you're stuck in a very bad situation...

Here's what I'm thinking has happened:

For whatever reason, the device was bootlooping on the official firmware, possibly due to root, possibly something else. This part I honestly don't know about (yet).

You flashed the custom kernel which did indeed let the device boot, thanks to the sm_verity being disabled.

Because the phone was upgraded to 5.1.1, the new Factory Reset Protection (enabled by default, but can be disabled in the Developer Options -> OEM unlocking) was in effect.

Unfortunately the mistake that was made was pressing that reboot button. It flashed the stock kernel back onto the device again.

For whatever reason, this is causing the same bootloop again.

But the problem now is, FRP is enabled, and you can't flash the custom kernel again to go turn off FRP.

So, you're probably thinking, "now what?" ...

I'm not sure. Theoretically, flashing the proper Odin package is supposed to fix these kinds of things. I don't know why it's not, and why some people are getting bootloops. But again, I have seen a lot of posts from people who have done certain forms of carrier-unlocking, and it's breaking the phone. I believe it's something to do with the EFS partition. If you had a G925T, I would recommend checking out this post, but I'm not sure what this guy is doing to fix the problem. Perhaps I'll download it and compare it to the stock G925T OF6 Odin package and see if I can spot the difference.

Another option is trying to flash the G920T Engineering Bootloader, if you can still find it. It was posted around the forums here, but most of the links have been taken down. You're looking for threads/posts that explain how to root 5.1.1 without tripping Knox. If you can't find it, PM me and I might have it lying around here somewhere.

Apart from those options, I am not too sure what to say. The combination of have a stock-boot-loop and FRP being on... is not a good one.

Edit: Interesting... That "fix" is simply the same stock Odin package, but re-packaged as a 4-file flash. The AP_ one only includes system.img and boot.img (ROM & kernel), and then the BL_ one only includes sboot.bin and cm.bin (both parts of the bootloader).. CP_ has the modem... and CSC_ has the cache and recovery images. In the "fix" instructions, he instructs only to flash the AP_ and BL_. He also instructs people to wipe stuff using the stock recovery, but I don't know if that's necessary or not.

My guess as to what's going on: The cache.img might be breaking it. On the G925T, when flashing the OF6 stock package, it flashes a "pending update" (not sure what exactly to call it) to the cache. Upon first boot, the stock recovery installs the "pending update" onto the System, and then reboots.

Three things you can try:

1) Flash the full Odin, but reboot straight into Download mode (odin) again after it reboots (you can do this by unchecking the reboot option, and then forcefully rebooting when it is done flashing, and boot straight into Download mode again). From here, flash TWRP, and maybe the custom kernel while you're at it. Reboot directly into TWRP recovery, and wipe the cache.

2) Repackage the Odin package to exclude the cache.img.

3) Repackage the Odin package to exactly match the "fix" (4-file) one in that thread, and then follow his instructions.

Edit2: Never mind about flashing TWRP - forgot about FRP. Crap. I'm thinking you're going to have to repackage the Odin file without that cache.img, OR you're going to have to try the engineering bootloader.