I tried it in both roles, client and host and it works always fine for me.
I can not replicate this issue, but we are happy to take another look,
if you have any more detailed steps to reproduce the problem.

Right now we just do not see any issue with this.
Cheers

Halle Dark Matt,

The Haste potion is actually working but only on hosts simulation.
When a client used it the minions did not speed up visually, but on the host they did.
So when rallied under Haste minions were first not moving faster  but get finally teleported ahead because their speed didn't match the host.

We make now sure this speed up is probelry networked, so that the speed up is visual on client sides rather than doing a strange teleport.

I tried to spawn a Behemoth while being client and dismissed it by giving it three slaps. 
But I'm still able to summon an Archon afterwards:

So the steps you mention are not enough to reproduce the problem.
If you can find reliable steps to trigger the issue, we are happy to take another look.
But since all works when we try what was mentioned, we can not make progress on the issue until we have a way to reproduce.

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!