This has been an ongoing problem for several years. We have never been able to reproduce this, and we have to be able to reproduce the problem to find it and fix it.
Here is what we know:
The problem is intermittent. If Rhino hangs, then repeating the same intersection again will work correctly.
The hang is very model dependent. The problem is not with the intersecting surfaces, but something about the entire model. It has been nearly impossible to get anyone to submit a complete model to us when they have a problem.
From your reports, I can see that Rhino somehow gets deadlocked, but the deadlock doesn’t make sense to me, and I cannot see what causes the deadlock. An intermittent deadlock also means that two competing processes just happened to interfere with each other, but this does not happen every time. We’ll need to reproduce this in our debugging environment to see what is happening.
We need a somewhat reliable failure to be able to find this. We need a model that we can run Intersect on, undo it, and keep redoing it, and that the model has at least a 10% chance of hanging. If anyone has such a model, send it to us and tell us how to reproduce the hang. We also need your Rhino info so we can try matching the hardware you are running on. CPU speed may play a factor in this.
@bigjimslade I see a couple of things in your reports that complicate this request. You are running 10.10.5, a three year old version of macOS. Our development and debugging software requires 10.13, and that’s where we must be testing this. You’ll need to upgrade to 10.13 to confirm that this problem still exists on 10.13. Second, you are running Avast on your eight year old Mac. Macworld says that Avast slows down your computer considerably. This may be contributing to your Intersect problem. We won’t be installing Avast on our computers, so you’ll need to disable Avast and confirm that you are still getting hangs in the Intersect command.