Hello, So Ive recently built my machine, and used up one spool of filament tuning it.

then I've bought the same colored PLA from the same supplier, and the same brand. aand now my prints get some really under extruded layers every 10 or 20 layers.

I've been trying to lower the layer height, then increase the extrusion multiplier, but nothing seems to work.

Any ideas?

Have you measured the filament diameter?
I have many spools and they are all a little different. It doesn't take much to not be right anymore

well its 1.78 so pretty precise, as i hear others get filament that is 1.32 and 1.87, so 0.003 offset, shouldn't make that much of a difference should it?

If anything, you'd be getting over extrusion.