I have had consistent problems when double-clicking a block to edit it, Rhino often crashes when this happens. I get around this problem by exploding the block, editing it, then creating a new block with the same name overwriting the old one.
I discovered that when I copy the block into a new document or delete half of the objects in the file I can open it, but I don’t think my file has an excessive number of curves and objects (3092 curves, 109 block instances, 11 hatches). In this file I uploaded I have deleted some objects from the file but Rhino still crashes when trying to edit some of the blocks, though in this file some blocks can be edited with no problem one time, and cause a crash the next time I open it.
I am running Rhino 5.2.4 on macOS 10.12.1, on a late 2013 Retina MacBook Pro.
test.3dm (2.2 MB)