Low compression

Hello, I have a misfire on cylinder three, the spark plugs have been changed coils checked
Carried out compression test, cylinders 1, 2, and 4 are 15 bar.
Cylinder three, 9 bar.
This fault running on three cylinders is intermittent. The other thing I have noticed is when it runs right the engine light stays on constant.
When the fault occurs the engine light flashes.
Any advice would be greatly appreciated

Regards,

Mark