Yep, I get this too on my warden healer. Happens every time after the harvester boss in WGT. I always have to wait like 10 seconds before going through the door because for some reason I'm still in combat. I actually watched for it once and it left combat for a few seconds then immediately went back into combat. I ran for the door, had the prompt, USED IT, then I was back in combat and it canceled my action so I just stood there lol.