As Leo's said, the problem is that any attempt to access (which includes things like, obtaining timestamps, file attributes, filenames, icons, file types, etc..) an unavailable network drive can result in a freeze. The only solution is to move the action that triggers it to a background thread. We have moved many things to background threads already, but it's possible there are still others that could be changed. That's why I said "identify specifically what is in your configuration that's causing it". Maybe it's a toolbar button, maybe it's having the folder tree open with a particular combination of flags, maybe it's the result of a shell extension you also have installed. We need specific information that will let us identify where the trigger access is occurring.
Sending us a process snapshot from when the freeze occurs can also be helpful.