We consider 16 GB under reasonable limits for practical image processing requirements. See the
System Requirements page, RAM section, which we have updated today.
However, the problem reported here cannot be caused by insufficient memory. That does not make any sense because thin plate splines have small memory requirements in the range of several megabytes at most. The new DDM surface splines require more memory than the old traditional splines, but only several hundred kilobytes more. This cannot make any practical difference.
To be honest, I have no idea of what's happening here. All of the images uploaded for testing can be solved perfectly on all platforms, on all machines, all the time. Zero issues.
We have managed to get access to two Mac machines with 16 GB and 8 GB of RAM, and will make tests on them.