This guy has a video of the guys not getting into the firetruck during A2M15. He doesn't know how to replicate it though. Maybe someone can figure it out, or it's completely random.

This glitch was replicated by me and fiku a few months ago:

I still don't know exactly what causes the fixer(s) to not get inside the firetruck. My best guess is that it has something to do with how the enemies are killed prior to the firetruck cutscene. It could be both RNG and timing related because the fixers don't always spawn in the same spot.

A different way of getting the firetruck skip was found. This was also posted in the strats thread and is very consistent: