I noticed leetle "sub-chips", and that might be the problem.
As box tools take such a huge "bite", the chip
(if run with no chipbreaker, and make a huge spiral)
the inside is much different length than the outside, hence the spiral.
Sometimes the material can hold it all together, other times not(think cast iron how it crumbles easily) and you have the little "entrails".
I would change the tool out to a piece of HSS, ground really sharp (you are machining free machining steel, so tool life is good) and no chipbreaker.
Look at older box tools with HSS bits, and you'll see the top
is angled back and down as well (not a flat top).
So what if you get a big long spiral ? If it all stays together,
you don't get little pieces under the rollers.
BTW When I suggested "Flood coolant" I mean using a piece
of copper or steel pipe to direct it right down in between
the rollers, pour it on so much you can't see the complete box
tool. A couple of my box tools came this was, firmly clamped
in place to keep the outlet aimed correctly.
The point is not so much lubricant, rather to flush the chips out fast, before one can get on a roller.