Sometimes shavings get humps and valleys in, other times they wind up into neat little toilet rolls. Is this indicative of anything? Seems like a lot of variables.
I'd have a guess that issue is because of unsupported work deflecting.
Beware if wanting to get to the bottom of the dips, as there is much chance of making a big convex mess, obliterating the perimeter of the tool, and there's no way to fix that without targeted removal
which has to be some method of abrading such as a small block w/abrasive or a smaller than the area of the plane sized piece, in order not to remove metal from the perimeter.
You might have a real good surface plate of sorts which your using.
If you had two pieces, you could see what your doing, so just sayin incase you think
an even scratch pattern means flat.
That doesn't mean a thing.
How's about tuning your plane instead of lapping the sole?
i.e hone your cap iron like the very few who actually use it, and not take any suggestions otherwise,
and make some
straight shavings as you'd expect a smoother to produce.
Much different from the usual folks who choose to not see a plane working like it should.
Best to get this down early before you get too caught up in some singular gurus, money making rhetoric,
as you'd find out most of those utubers aren't honest like they would make you believe.
Straight shavings is the sign of the cap iron working,
and that's the pinnacle of making a hand plane souped up, i.e cap honed at
50 degrees or greater.
and don't break the
three rules when you do!
(it simply won't work if you try doing your own thing)
Forget the rest of the red herrings, and see how it performs with some of the best lessons from St David Charlesworth.
Choose his methodology on things, and lessons on accurate planing,
and combine with actually getting straight shavings from the plane,
and by that I don't mean Cosman either, but from someone who makes use of the cap iron instead.
If you don't see shavings straightening, then you're not looking at what you should be watching, simple as that.
An example for you, which should be enough to weed out plenty of gurus concerning hand planes.
Enjoy
Tom