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It is a known issue. The first boss moves between waypoints and if something throws it off the designed track it can easily happen that it gets into a place where the movement code fails to get it out again.

The second one can happen with any monster if it overlaps with blocking lines in a certain way. Hexen makes this easier because it allows to alter some map properties through its scripts. From the look of your picture it is stuck in a blocking line.

Both the bosses in Hexen so far have gotten stuck, allowing for no challenge kill. Now this may happen in non-gzdoom version, And probably does. I do not know.
I can't be bothered to sludge through the old Hexen just to find out, but perhaps someone has some ideas, to prevent this.
My idea for the second boss is a short range teleport or awesome "phasewalking" ability lol. As he seems to get trapped. Or, reduce his size in the engine (not visually though).
Having trouble figuring out an Idea for the first boss since his inability to make sharp turns is his weakness that you are supposed to use to defeat him (or so I read)

I made a couple maps showing how they got trapped when I played thru. Not the best but easier than explaining

First boss completely stuck and not moving or even animating.
Second boss stuck behind staircase and cant figure out a way through or around. :roll: ... but moving a little and putting up his shield...

Any ideas? thanks for reading
[attachment=1]bossStuck1.png[/attachment]
[attachment=0]bossStuck2.png[/attachment]
yes i do have an art degree :lol: