Has the same hardness as the rest of it. I wonder what could it be, then, from the tree growth point of view. Looks interesting, thanks to the fact that the board has a very rapidly increasing runout towards the end seen as getting darker, on the pictures. Maybe it was closer to the basis of the trunk.
If you have a board that is already flat run it through and see if it stays flat. That will tell you if the table need adjusting.
When face planing I usually run the first pass with very little pressure so that I don't bend the board. I want the part that are naturally in contact with the table to be cut first. If the board is riding high on opposite corners I try to "balance" it on those corners for the first couple of passes. If your first cut can be as deep as the corner gap under the board, you may take the twist out in one(maybe 2) passes.
So what color light do your bulbs give out? I have 4 - 4 tube x 4 foot fixtures with T8's and I would like it a little brighter and a little more like natural light. Don't think that I will spring for new fixtures but if I can put LED's in my current fixtures I will.