If you fail the part with the two seals on first try, all the mobs stay in place, which makes it a lot more difficult to complete.
In a perfect setup with all experienced players it can be done within a few minutes, with a subpar group this is nearly impossible.
My question is, is this working as intended or is it bugged?
Also, you probably know that the endboss sometimes buggs out if you stay up close when he drops the Mc Hammer!?