Hi Paul -
Did something change on your system? New GPU drivers, Windows update, …?
Please run the Rhino SystemInfo command and copy-paste the result here.
When Rhino freezes, you can create a manual dump file and send that to us. You can find instructions on how to do so here → Manually Creating a Memory Dump (DMP File) from an Unresponsive Rhino for Windows [McNeel Wiki]
-wim