Guild Wars 2

So, I got disconnected when the boss had around 10% HP left. When I was back, I was lying dead on the waypoint. I received the loot and bonus chest, but Aetherpath didn’t count for achievement.

You can try contacting customer support though most likely they won’t be able to help. Opening a ticket is done by following the support link on the top left of this page.

Is there any difference if I open ticket via in-game support or forum support?

Yes the in game is not so much a ticket. You can’t track it or get in touch with anyone regarding it. The website one will give you a number and you will get a response