I was working with planer trying to get a right thickness for top of a workbench yesterday. Bottom of the piece was completely flat and sanded before. Imagine my surprise when me and Mike find a deep grooves there. So apparently someone drill a holes in the support holders and metal had a little bulge which was causing an issue.
I piled down and sanded as much as I could and it worked fine right after.
Big shoutout for @Gibbtall - your planer pipeline worked out just great!