Hello - for now, select the original mesh, Invert to get the flattened version and then RebuildMesh on that. I’ll see if I can reproduce the problem. @slaterr - this is a bug that has been fixed recently - https://mcneel.myjetbrains.com/youtrack/issue/RH-62531
This fix may be in the 7.5 release candidate now available:
you can get the fixed (7.5) version by changing the ‘Update frequency’ in Options > Updates and Statistics page to ‘Service release candidate’