What you have there is a good example of an expansion chamber as designed by Hiram Maxim. It allows the gas to expand slowing down the flow. I've attached a gif but just imagine that each bullet is the pulse from each cylinder, the slow down causes back pressure helping to control/slow the next pulse in turn. The bleed over is just accidental in the resonator or the baffle plates would have specific holes for the gas and not just pass through holes for the exhaust pipes.

H/T: silencerco for the gif

Sent from my SM-A730F using Tapatalk

__________________
"When the Team Chief said.... You're trapped in a hole with nothing but a goat and a slinky, what do you do? Stubby said, I'm not sure but it won't end well for the goat...." ~(Overheard) Last day, Phase 3, Q Course