Thanks a bunch. Had I stumbled across tolerance would certainly have tried increasing it rather than making it smaller to ever greater frustration. I set it to 0.0001 as you suggested and it corrected a number of addition problems.
I have been collecting all my migration notes and have added this to my list.
I also encountered the problem of getting an error about manifold-edges. In the videos I see there is a check edge command but apparently the Mac version is missing the manifold edge check.
That said, I discovered that making the tolerance smaller adversely affected adding some parts. I have attached one example here.
Problem 5.3dm (512.2 KB)
Would it be normal to change the tolerance or does the fact that this requires a low tolerance indicate a part problem that I do not see?
Oddly, similar jagged parts add only with low tolerance but the ones here require high tolerance.