Okay, this is the last level I started to play of this scenario, and I do remember the completely invisible Devlin, but I never got any further than that. Now, on this film, there are at least two bad mistakes you made. First of course was the switch you didn't notice getting toggled by BS' Shotgun. However, you did make another one in your solo play. Namely, you could've gone back to the 2x Charger after getting reduced to a sliver of health after having already reloaded and redone the entrance to the ship, but for some reason thought (and said) you couldn't. At the end of the 2x Charger room there were those stairs that led to the corridor with the broken-down wall. Couldn't you have just gone back up those stairs from the other direction to get to the double charger?
Anyways, yeah, this scenario is clearly Evil. ;)