OMG! There is a chance I might have found a solution to the lockup bug! I've got a report from the standalone version of app verifier (which I've never used before) from a remote machine along with a single stack trace showing an error. Because I'm not experienced in how this version of app verifier behaves I can't say anything for sure yet...
Using that info and trying to see how it could have gone wrong I've come up with 2 changes that might fix the problem I think is occurring and it's a race condition that exists in v5.x.x as well. There are no guarantees that this is the lockup bug at all, but it does involve a socket which all the dumps seem to indicate is involved in the problem so I'm hopeful!
Unfortunately I'm still trying to finish up the next release so it will be a bit before we can play with trying to prove this helps...