Cylinder misfire and judering

Question

Hello, i have a vw golf 1.6 16v 2003, it has an intermittent misfire or running on 3 cylinders, the obd diagnostic says cylinder 3
I have compression tested with these results Cylinders 1 2 and 4, 15 bar cylinder 3 9 bar
The engine light is on constantly, it flashes when the engine is running on 3 cylinders, you can hear a popping out of the exhaust, the spark plugs have been changed, the coil packs were checked and thats all the garage did, they just said they didn't know what the cause was
I would greatly appreciate your advice on the problem

Regards

Mark