Back Pressure
The propellant gas a suppressor pushes back toward the action, which can increase fouling and disturb cycling on gas-operated rifles.
When a silencer traps expanding gas to quiet the shot, some of that gas has nowhere to go but back down the bore toward the chamber and action. This rearward flow is called back pressure, and the more restrictive the baffle stack, the more of it a can produces. The effect is mostly harmless on a bolt-action rifle, where the action stays locked until the shooter lifts the bolt.
On a gas gun the consequences are larger, because the same gas that drives the operating system now arrives sooner and at higher pressure, which can speed up cycling, increase fouling in the receiver, and blow gas back toward the shooter’s face. Modern low-back-pressure suppressors and adjustable gas systems are designed specifically to tame these effects so a semi-automatic runs cleanly while suppressed.