Reply by lab7654

The marks are most likely due to the rollers rubbing on the board and not feeding it properly. Check the rollers for wear, maybe they are just worn down too much and can’t grip the stock. Otherwise it may be the wood. The sap might be sticking to the bed and not letting it go through smoothly. Try waxing the beds and scraping off any sap you can before planing.

-- Tristin King -- When in doubt, sand it.