Location: Tyranid Datahunt level 35(?) mission @ boss fight (forgot the name of the boss sorry, located in the map above). The boss looks like a towering green spider with green gas around it.

How it happened: Facetanked the boss with my Heavy Bolter (Crusader - Tactician). Then, when my character was Overwhelmed, the boss casted a green goo on my char and rendered him immobile.

Other details: While immobile, I can still use an Innoculator, and change weapons. However, I cannot move away, attack with my weapons, use grenades, or cast any focus skill. The rest of my party had to complete the mission without me.

This bug has happened to me twice so far, both times I got stuck in the same green acid/goo.

Edit (27 Dec 2019):

Encountered the bug again yesterday - managed to screenshot the Tyranid boss this time. Dying and resurrecting fixes the "stuck" issue. All 3 bugged encounters so far has happened in multiplayer.