I went to the Armouring Hall, ran the assault trial "Death From Above" several times, exited to battle barge using Finish Trial, and I found 3 of the sniper type tryanids having spawned with me. I was shot until I died on the battle barge, and I had to quit to title because there is no respawn on the battle barge or method to get rid of enemies there.
I experienced this a second time in a row by following those same steps, and curiously the enemies didn't spawn in on top of me until I moved. I stood there for several minutes working on my my other monitor, and only when I came back and made a small movement did they spawn in.

On a 3rd time when I was able to recreate this it appears the spawn is timed, and it took around 20 or so seconds before the tyranids would spawn.

Pictures attached are me being shot by them before I was forced to quit to title.


It's interesting the types of enemies that are spawned, it's 4 of the small ranged tyranids, but in the trial there is also an elite type that spawns in a second wave, but this enemy never does. I have not tested this on other trials.