This problem has existed for a long time and is presented randomly with any surface and polysurface.
As the intersection is a command that I use often I adopted the following strategy: 1) copy and paste on a new part files that need to be intersected (I always keep an open file empty for this). 2) in case of cut surfaces, use the command “UntrimAll”.
3) place normally do not show blocks or slowdowns with this strategy, so once obtained intersecting curves, copy and paste in the original file.
Sometimes I forget to use this strategy to save the file before you use the command and Rhino crashes … This happens at least 2-3 times a week and often results in the loss of the last 5 minutes of work.
The problem appeared already two years ago:
Intersect freezes rhino
Reported but no luck (Rhino seems to have its own life in my Mac? 
)