This is quite old, but maybe it will help someone.
These “cracks” are result of groups of images of the same area that are not tied together properly.
This results in 2 (or more) surfaces very close to one another.
RC then changes (sometimes erratically) between the two, depending on the quality and/or coverage in a particular spot.
In my experience, this can be only remedied by adding control points, if it is not possible to add more images.
Sadly, that can easily get out of control in terms of time because often if you fix one spot, another gets thrown out of whack a bit.
Would be way easier if there was a filter for reprojection error, which in my cases takes care of this problem…