I tried various quality settings up to the limit of what my Mac could achieve and that did not resolve it. So to test if it had anything to do with the presence of the three orbital sweeps over that area, I painstakingly removed all the relevant orbital photos and got a reasonable result as here:
The orbits are still present at the further end, over a smaller holed stone but, for future reference, my query is how can the presence of the orbital photos make or break this model? I was under the impression that the more photos the better for the model, even if there is a degree of overlap in the camera positions.
I also wondered if the setting ‘PC Rectify’ would have helped ‘fill holes’?
Just for interest, I include here a closeup model of one of the stones in this larger area model:
The three orbits that I removed from the photos were all at -45 degrees (to the horizon) and of different radii, heights and centres of rotations. If I’m only 10ft off the ground then my gimbal might be -20 degrees.
For all my previous surveys the orbitals have only added extra detail and have never resulted in big holes in the ground. Strange.
Normally I include 3-4 orbitals of different heights, radii and even heading direction. So in this model of a stone circle, I had one orbit tight around the central stone and another inside the circle of stones looking outwards to give detail of the inside surface of the stones.
I have posted this link before but it’s relevant here to your enquiry: