[Hectic]

not sure how the recoil spring will have anything to do with the gas venting.
somehow the valve knocker is hitting the valve, thats the only way to vent the gas. Seems a lil odd (tho im not all that familiar with the CZ pistol so not quite sure what the internals look like but there has to be some sort of disconnect that moves the knocker back when the slide is racked. So either that part is worn/broken causing the knocker to either stay forward or get pushed forward when the slide moves.
i had a simaler issue with a glock before, the lil loop that connects the knocker to tue hammer was brokes. Gun would shoot fine sometimes, sometimes would vent on mag insertion and sometimes vent on slade returning to battery.
id have a gun dock lool at it personally