Im sorry I just happened upon this.... No sir I never got that problem at all while working on this one.... I haven't read every response, but I could go back to the last spot you were working on before you saw this, Draw a very large circle around that area and drop it.... I would pick up all the shapes within this and then do a simple smooth a couple clicks on that original shape you drew and dropped then optimize at a minimum setting.. Redrop everything
Ive also had this happen before on a simple shape, and inflating it or deflating it an inch or two fixed it...
Hope you've got it figured out, I was interested to see how you've done with this plot....
If I reposted what someone already has I apologize

Terry