This happened in the Cold Plains. Running in circles, I observed the rock on the right disappearing and reappearing. See screenshots:
hxxps://freeimage.host/i/R0gzas
hxxps://freeimage.host/i/R0gu9f
hxxps://freeimage.host/i/R0gI8G
hxxps://freeimage.host/i/R0gxFn
hxxps://freeimage.host/i/R0gAu4
hxxps://freeimage.host/i/R0gRwl
hxxps://freeimage.host/i/R0g5t2