Zooming in on the loop in Smarandache Sequence

What is going on in the loop here at the bottom right that causes the turtle to change direction? In the Ten thousand digits path it is some of the orange and light purple parts below

to draw just this loop part of the image the code is here. Zoomed in the path looks like this

This image contains the 279 primes from 14503 up to 17183

In the 100K image it seems to be the over 2000 primes between 152003 and 178361 that make up this loop part