Oak cabinets need to be primed with BIN shellac primer, or oil primer, to prevent bleed-through. There are some newer BIN products like the advanced synthetic version, which I've never used. I use the regular BIN shellac primer and never had any problems with bleed through. Cabinets also need to be sanded and cleaned to remove surface contamination. Sometimes there will be a few tannin spots on a couple doors that the primer didn't completely seal. You can use a spray can of oil primer to spot prime those spots. If there's tannin bleed everywhere then it sounds like the wrong primer was used and the doors would need to be primed again. If the grain wasn't filled too, that might be part of the problem. Filling the grain fills the deep valleys and cracks in the wood that can be difficult to work the primer into when spraying. A coat of grain filler levels out oak. You can also try spraying a little heavier as it's possible the primer isn't seeping into the cracks enough to block the tannin.