Unable to complete Frostmourne mission

Having issue with not able to complete the last Human Campaign. Currently game patched to the latest update. After completely clearing the entire map of all enemy bases, mission doesn’t end with a victory. Noticed Malganis was situated near the destroyed altar of darkness on the northeast part of the map and I am unable to hit it as it’s armour showed indestructible. Please advise. I have restarted this mission countless of times. Currently playing on hard difficulty. Thank you

Did you, at any point in the play-through of the mission, load from a checkpoint save? Meaning, when you say you started over, did you start from the very beginning of the mission and play through in one session?