Tannin

Tannin bleed, also known as tannin leaching, occurs when tannins in wood migrate to the surface and cause stains or discoloration. This can happen when wood is painted with products that don't trap tannins, or when wood is painted before it's fully dry. Tannin bleed can also occur when wood is exposed to water, including water-base paint without a sealant or coating.
Tannin bleed is most common in woods like oak, redwood, cedar, and mahogany, but it can happen with any type of wood. Tannins are natural compounds in wood that give it its brownish colour. They are water-soluble, so moisture can bring them to the surface and cause stains, specifically when refinishing and painting wood products like cabinets, doors, trim etc.
To prevent tannin bleed, you can:

Prepare the surface: Degrease, sand, and repair imperfections
Use the right primer: Stain-blocking primers can neutralize tannins