Found another bug! I used the Gunslinger ability that puts a bomb on an enemy which then deals damage to every other enemy when it dies, and when it died, it wiped out the entire wave, bringing in the next wave. However, as you can see, the timeline is...far too crowded for the three enemies on screen, and this does manifest in giving them extra turns. Kind of a huge difficulty spike, though I did manage to tough it out.
Update: I think they're actually layered on top of each other? I killed the robot, but it was still there and its lifebar was a different value. Maybe it triggered two waves at once? Hard to say for sure.