Piston ring gaps sometimes line up and allow leaks, but never the same cylinder twice, helluva coincidence if they did. And they would sort themselves out after a hard run.
I would pull that cylinder off and have a look. It's not impossible to refit the thing with a ring missing altogether, or cracked while fitting it. No disrespect to your maintenance crew but it is possible.
If the plugs are fouled up after an hour it's definitely not behaving as it should, rings, valves, valve guides/seals.