hi Guy,
not sure I can help here, but have some thoughts, I may disclose, with more info...
can you add a screenshot , to this post showing, the 'Outliner' window with as much structure of a failing .skp, showing as possible.
I have tried the standard instal ruby with some 'group sorting' problem scripts and it didn't appear to help, your milage my vary, but I think problems on the 'C' side...
So, other then the usual, general advice,
Close all supplementary windows, eliminate 'SU' trying to refresh the view, ie have it really small, on an empty scene.
If you can provide a snippet that fails more advice could be given,
john