I'm using a current version of VEP 5. I run the slave on an Asus (quad core) w/ Windows 7 and the main computer is a MacPro 12 core (OSX 10.12.3) with Pro Tools 12.7.1. But this problem has been going for a year or more throughout other versions. If I load VEP and one by one build a session of Kontakt instruments, Omnisphere and some others, everything is great. If I save that and come back to it later, trying to play either a new track or just add to an old one will be full of latency and notes choked off similar to what too many voices might sound like. Small or large number of instances doesn't seem to matter. It will behave this way with 1 track in 1 instance or 16 tracks in 3 instances. It will play just fine. But recording is the problem. Close it and create a new instance of the same thing and the problem is gone until I save, close and open again.
I've changed routers. The router does go to the internet. But I get the same behavior if I connect the PC straight to the Mac; bypassing the router. I've tried various buffers. And I've double checked things like midi in the Mac. Midi thru is on, but there are no midi loops through the controller. In fact, there's no midi in to the controller at all. I've tried another key controller; same thing. I've tried midi as opposed to USB; no change. And I'm certain there are no midi clocks or large amounts of sysex being sent.
Other than trying (and learning) Logic, I'm at a loss as to what else to check. Maybe someone smarter than me can make a suggestion.