[Gaps in circles]

I'm having the exact same problem.  other than concentric circles the print looks good.  I did a test part and pealed the concentric circles apart like onion skin. the circles measure 0.38 mm.  i extruded a sample from the tip in free air and it measures o.48. I'm not sure where the material is getting lost. Can anyone help further?

 

[Holes appearing on STL model are ommited at impression.]

I had the same problem.  Working in Sketchup, slicing in cura. When slicing in cura the holes were filled.  In the setup, fill holes was not checked. The problem was reverse faces.  I flipped them and it's all good. thanks for the help