get_compressed_copy is found where?

if (hasattr(x, 'get_compressed_copy')):
                 compressed_x = x.get_compressed_copy(mask)


You added the snippet above to axes.delete_masked_points as part of one of your massive "units" patches. It needs at least a comment in the code--which I would be happy to add, based on your reply--because I don't see any such attribute in mpl or numpy. My guess is that it is specific to the JPL array-like objects which motivated the units support.