Rare Monster can't be hit making map uncomplete

I had this happen on a map a day or two ago and wasn't a huge deal but now I am on the Stone Citadel and there is 1 Monster left and its a Rare I can't hit the mob so I can't kill the rare which means I cannot complete this map.
I did kill the boss which gave me credit for the quest here.
bug reference 3,749,386,476
I took a video using moments by steel series and also got screenshots.