I think I was hasty on my initial testing and post -
Vojtech was on my issue (very impressive by the way) - and I tried to load up the VST3 to see if I could help him and get it to work by boosting the latency a hair. Wasn't necessary - I loaded, routed, and it worked fine. I really should have rechecked the VST3 after finding that the VST2 worked fine.
Weird one but it seems to work fine here -
Sorry if this created some potential concerns among prospective users - This really is an excellent vocoder.