I was doing the final quest of the game in act 3.

There is a quest where you have to get 3 different hearts before you can fight the final boss. After I got two hearts, it told me to go to the place near the starting area and let me progress to the final boss.

After I completed the final boss, I went back and was able to fight Seth and Nyleth.

I am wondering if this was a bug in the game or if you only needed two of the hearts to progress.

If it is a bug, I wonder if it occurred because I fought Seth a few times and gave up to try the others. Maybe it marked it as complete.