I'm printing with PLA on a "PEO" print bed (really a textured PEI), on my heavily modified ender 3, and there's a pattern on the bottom of my first layer that I'm trying to get rid of. The top of the first layer looks fine, and changing the z offset in either direction doesn't help. I've also tried slowing down the print speed because I thought the extruder might be skipping, but I'm still seeing it at 10mm/s. Any idea what could be causing it, and how to get rid of it?
I would have guessed the same as others that it was interactions between the nozzle and the bed or some texture on the bed. Especially since we don't see any normal extrusion lines which are normal on the first layer.
Since you're confident it's not, are there artifacts elsewhere on your prints that might be a clue? Is there anything going on with your nozzle? Maybe some wear, chips,or inconsistent flow? If you print just the first layer what does it look like from the top? Does it help describe what we're seeing?