I tried this now for quite a while in various ways but I can not reproduce such behaviour:

I only have one Ember Demon and without any mnore reliable reproduction steps, we are unable to see what was going wrong for you.
However if you can find reliable steps to trigger the issue, please let us know.
Just holding an Ember Demon in the hand seems to be not enough.

The issue will be fixed for next patch.
Basically chasm is a collider, banshees got spawned below and could never reach the up side of it.
We made now sure it lets things through which want to go upwards.

Thank you for letting us know about the issue!

I can see those minions in the save, but I have no idea how they can end up in this state. 
Their ability to take part in fights got disabled, this happens for example when units are put on props eg. torture,
but when ever they leave these props this is reset to normal.
Some error must have prevented their reset, but I do not know which.

Unfortunately I have an hard time to fix.
I see the tile is there and has no claim task but what I would need to know is how it got to this state.
Some error must have prevented the creation of the claim task, but I do not know which error and how it happened. 

I was able to identify the cause and fix it for next patch.

Better late than never: This issue will be fixed with next patch :)