If I open a VST Duende plugin the "track view" will graphically stutter/step. The mouse will freeze & jump. But only over the trackview. Dock, inspector, console view is fine. Odd..

The plugin is probably hogging the UI thread and windows message queue. I suggest reporting this to to their technical support since there isn't much we can do to address it..

Just submitted the issue to their team.
Duende plugs have a rough coding history & i'm sure you're correct, but this is X3 specific. X2 & other DAW's handle it fine. 

Wait if you do see different behavior in X2 with this its worth us investigating so submit a CWBRN..

Submitted - CWBRN-20373

Are the VST3 versions working for you Eric? I can insert them but they aren't doing anything. Licenses held on Reason codemeter stick.
 
Not sure I can replicate the slow performance glitch you are seeing but one thing I have noticed is stuttering nowtime during playback if snap is disabled and aim assist enabled.

Nope, the vst3 ver seems broken. Meters show mystery signal. Are you getting the same graphics issues as I am?
 

At work sorry but I'm sure I would have noticed that by now.

I'm using an Nvidia GPU, are you ATI based?