I submitted an ingame bug report for it, but I also wanted to post it here so other players are aware. The Branded Wyvern boss went sentient and invulnerable (see Nov 30th patch notes) on me at 25% blocking progression. Needs more Turing tests.
I'm sitting in the instance right now, beating on an invulnerable wyvern stuck at 25%.
I booted up the instance and I cannot even target the Branded Wyvern. All the NPC allies just stand around, not doing anything.
I am stuck at this same 25% mark now, same as in the screenshot above. First time doing this instance.
I just repeated the instance a second time and it worked.
This just happened to me when the Wyvern reached 2/3 health. I also sent in bug report.
I bought LWS4 started it and realize I have no way getting there to start it. No WP. Can't swim over due to 'strong waves blowing you back'. Come on!
Have you tried the boat?