Quest Targets respawning. Bosses disappearing

[ibol]

Fennrick,
To my knowledge I do not experience either of these behaviors.
However, I will try to re-create both this weekend.
(I am not saying you are mistaken, I am approaching it from an empirical viewpoint, with a mind to what would cause that.)

And about achievements:
Remember that If you are playing without perma-death, then no achievements will register. One of the caveats to the hardcore.