Staining on Freshly planed Oak

[petertheeater]

Just planed up some Oak. All bought in the same place at the same time and have noticed marks. They almost look like liquid was spilled on them - it wasn’t. Even though the boards are different they all seem to have the marking. It’s not uniform enough to be from sticking. I’m pretty sure I’ve noticed this in places on oak before but not to this extent. Any ideas?

I can’t use them like this as they are worse with oil finish.