In most cases especially a kitchen; it's what’s on the ceiling before you start the job that causes the problem and 9 times out of 10 it’s grease; the closer you are to the cooking sauce the worse it can be, extractor hood or not.
Before you start any paint job always give the area a wash/wipe down with a degreaser; sugar soap is one, if not the best.
If this doesn’t work, check out for an unusual sauce causing the problem. Is it coming from above, a broken seal in a shower leaking a very small amount of water, a weeping radiator ect.
Once you've scraped it back and washed the area with sugar soap, put a coat of oil based paint on the infected area let it dry (8 hours no mater what it says on the tin) and try again; this should sort it out.