Email from Agisoft support, thankyou.
Dear John,
According to the report file the overlap between the images is quite low and it may cause alignment issues that results in the dense cloud and mesh generation artifacts, and therefore will affect the final orthomosaic.
Actually, you can see that the lines of low overlap are visible on the last page of the report.
The recommended values of the overlap are 80% of forward overlap and 60% of side overlap.
Additionally, the problems may be related to the large polygons in the model, if quite low face count is parameter is specified.
Best regards,
Agisoft Team.