"The Will of Ashan" - "Heart of Darkness" [2nd campaign, 5th mission]

Finally, I made some progress. I created something so cool that I was amazed myself. Basically, I go to the ghost to receive a quest, then I go and kill the assassins, come back to the ghost, and the game shows the endless hourglass, while at the same time, I can see the troops in the castles and with the hero, but everything else is loading. I tried sending the assassins to attack the demon, but the same thing happens. After reloading the game six times, I gave up on the ghost, broke through the gates, and went to the castle (successfully defeated it and filled it with corpses). Unfortunately, I didn't get to use the portals, which is a shame because I was hoping to get the "Sylvan" artifact from the trees. Has anyone else experienced this?
By the way, in this last mission, Arantir developed to the level of Ornella, even though I had been leveling her up in all the previous missions.