Essence mobs despawned upon release

This one might be hard to reproduce or pinpoint.

As Witchhunter in the Valley of the Titans, I found essence mobs, placed Ripwire Ballista and fired Gas Grenades at them in frozen state as a random mob approached me. I quickly woke up the essence mobs but they didn't seem to appear, no drops were had, and the collision boxes of the frozen monsters are still on the ground.

Edit: Upon approaching the area again, debris on the ground rolls around for a second as if freshly placed.

Edit 2: Speculation: Ballista collision? Ballista was placed right at the center monster.

Bug Report ID: #2904482402
possibly similar situation for me:
giant skeletons as essence mobs in Valley of Titans
I cast Orb of Storms in preparation for third click
third click to activate, nothing happens. The skeletons remained as corpses; collision boxes still there.

immediately after, a new but similar bug!
Bug Report ID: #399932004
Walking Goliaths as essence mob
Desiccated Lich reanimated one of the Goliaths before the fight was activated; Goliath does not act, but cannot be harmed
activate essence fight; reanimated Goliath starts moving (and becomes vulnerable), but remaining Goliaths (including boss) don't animate, leaving corpses and collision boxes

note: did not use Orb of Storms this time