Weirdbits is on the money as I have also experienced similar with end grain on the edges.

Just need to go in the same direction as the grain for a while and in these shots that may mean a circular motion until the machine marks are gone. Once the machine marks are gone you can then run lengthwise along the edges with higher grits, nothing under 240 as you can easily add marks if sanding too vigorously coarser grits.