Here's my understanding. Semi-automatic pistols predominantly rely on recoil to cycle the action, in one way or another.
If you are firing subsonic ammunition, to avoid the loud supersonic crack, then you typically get less recoil[1] compared to a firing supersonic ammunition due to the reduced speed of the bullet.
In some firearms you can replace parts such a recoil springs to get the weapon to cycle reliably with subsonic ammunition, but if that is not done you will need to manually operate the action[2].
A few firearms even supports disabling the semi-automatic action, as the sound of the action cycling can actually be quite loud in comparison to a suppressed subsonic shot.
It’s possible he really downloaded some 158gr+ to get it as quiet as possible. To the point it wasn’t supposed to cycle.
Typically, though, you don’t necessarily get less recoil with subs. You get different recoil.
A 115gr 9mm at 1300fps as a sharp recoil. More than enough to run the gun.
A 147 / 158 / 160+ 9mm at 1000fps, has a lot of of the same energy, and typically a slower burning powder is used. It’s also enough to run the gun, the recoil is a lot longer and pushier instead of snappy.
I don’t know. If it was me, I would have my ammunition ready to cycle the gun. Yes, it’s a little bit louder, but the chance that I need to fire more than a couple of shots in order to achieve my goal and escape, outweighs the absolute sound reduction to me.
But, there is something to say that if I filled my silencer with wire, pulling gel, it was a big can, I have some ammo that I know won’t cycle, and I didn’t think I was gonna be in a place with cameras, yeah I don’t know. Maybe it was intentionally downloaded ammo.
If you are firing subsonic ammunition, to avoid the loud supersonic crack, then you typically get less recoil[1] compared to a firing supersonic ammunition due to the reduced speed of the bullet.
In some firearms you can replace parts such a recoil springs to get the weapon to cycle reliably with subsonic ammunition, but if that is not done you will need to manually operate the action[2].
A few firearms even supports disabling the semi-automatic action, as the sound of the action cycling can actually be quite loud in comparison to a suppressed subsonic shot.
[1]: https://en.wikipedia.org/wiki/Momentum#Classical
[2]: This can be more error-prone, if the action partially cycles.