Doing this with a group with a lot of less-experienced players. Our burn was slow. (Not sure if that is relevant.). We had a couple of wipes, but ultimately we got through.
The tank would, at times, lose aggro on the boss. It was his first time tanking that boss, but he is not new to tanking. He had no idea why he was losing aggro. I couldn't help him because I have never tanked any trial. I have done the trial on normal many times as DPS or heals in PUGs and don't recall losing aggro being a problem.
I realize that I am not providing as much information as might be needed to give a definitive answer to the question, but is there some mechanic involved with that final boss that causes loss of aggro. Loss of aggro had not been a problem at any other point earlier in the trial.
Thanks.