Well after nearly two hours, I can finally log back into the game, and the forums.
Similar issue to everyone here, got disconnected half way through the ‘destroy the trapped explosive gas’ part and couldn’t log back in, when I managed to (only for around a minute before another disconnect) I was in a different overflow with the event finished and the chest disappeared a second after I loaded in to the map.
After that second DC I haven’t been able to log-in since.
Pretty disappointed to have missed the final section of the end of the event and miss out on the rewards for taking part.
Hopefully Anet can find a way to sort something out for those that got disconnected, but I won’t keep my hopes up on that