In general, see the FAQ: Crash, exit or high CPU when viewing a certain directory
In addition:
Running Process Monitor to see what Explorer or Opus are doing when you expand the tree might provide some clues.
You could probably rule out the VPN / network issues by disabling all your network devices (which should prevent anything waiting on network requests and make them fail instantly instead).
It may also be worth temporarily disabling any real-time anti-virus scanning.