I got stuck in 05 Chance encounter. After I got the 8 boxes, there was a requirement for 10 enemies to be killed. The last one didn't show up. I think it might have died in the poison, or it just didn't spawn.
Thanks for reporting this. The game should count an enemy to the mission score, even if it dies of environmental hazards. If it didn't spawn, the game should only display nine pursuers as the objective. My guess is that it fell out of bounds, or the scorekeeping didn't count it for some reason. Both of these are something I've addressed in the development build. Unfortunately, the itch.io version is a bit behind. I've made a lot of progress, so I'm planning on updating the demo soon.