I was in the alliance. We were actively fighting it while the tank was redpearled. He was on Discord letting us know that he was relogging and to tell him as soon as his character disappeared from the game.

As soon as that happened, the dragon went white and someone else claimed it. It still had hate on us and was even still attacking us, but another alliance had claim.

I knew this was likely and tried to tell our 2nd tank to generate as much hate as possible before the d/c, but it didn't happen.

Just unfortunately Nasomi server BS at work. Several of our alliance members couldn't even see the dragon due to the insane number of people in the zone (for day 3, lol).

Lag is bad, but active tanks should never log to clear it. Wait til other tank has hate, disengaged, then log. You learn this during 120+ member Fafnirs/Nidhoggs.

I've depopped a KV because I hid on THF while I had aggro, and it instantly depopped, despite 11 other people currently autoing/casting on it. None of those other actions mattered, it force depopped. I know its not the same scenario, but there definitely are some strange bugs in the claim system.

Did some additional testing with a THF today. Last action didnt seem to matter with Hide. Whenever the THF was at the top of the hate chart and used Hide, the mob would go unclaimed even if other people acted on it last.

Correct, it's a hate issue not an action issue. See my previous post (about asking the other tank to grab hate before the MT d/ced).

Its a Hate issue for THF hiding, its an action issue for d/cing based on my testing.

If THF is top hate and hides, the mob goes unclaimed regardless if anyone else has done anything to it.

If someone D/Cs and is the last person that acted on it, the mob goes unclaimed regardless if anyone else had done anything to it and regardless if that person is top hate or not.

Two totally different scenarios causing the mob to go unclaimed.