Is the server slaved? When I first set up our slave setup I was getting a lot of dropouts, with an older server version .4580 (or something around that) but crucially I had "Internet Connection Sharing" enabled in OSX prefs to pass an internet connection to my slave machine. VEP really didn't seem to like the "Internet Connection Sharing", as soon as I disabled it I got dramatically fewer hung notes and audio dropouts. Now I've updated to .6150 and disabled Internet Connection Sharing I'm getting very very few dropouts and hung notes (still one every now and then) but this makes me very happy!!
In my Logic template I've set up a portion of my environment to send MIDI out to EVERY single VEP instance & channel and I've got an "all notes off" message at bar 0 on this track. So if I ever get a hung note, I just play over bar 0 and I'm sorted :D (or you can double click the MIDI out monitor in the Logic transport, but I prefer my solution).
Will