Sudden "sluggish" GUI issue

A project ive been working on for a while (today) for some reason causes the GUI and the whole program to act slow and unresponsive. I am completely lost as to why this would happen out of the blue. Only change I made was updating the Graphics Drivers, SO I rolled back. Same issue.

Other thing I did was update 4 plugins to their latest versions, which 2 are used in the project, now id roll them back too, BUT other projects that use the same plugins are not sluggish and making Cubase slow.

So what could possibly cause this ? Something is, and I can’t pinpoint it. Currently trashing preferences to see if that helps.

I find it odd that this project suffers and others dont. Maybe a VST in this one thats causing ?

EDIT : Trashing pref. didnt help.

BTW CPU use is 20% for the project, and disk load is minimal, buffer size is maximum. Really strange behaviour.

Think i’ve found the issue, was one of the updated plugins, I removed them all, GUI goes back to normal, so im reloading them 1 by 1 and it seems to be OK.

OK so that fixed the sluggish issue, but for some reason, this project seems messed up.

The GUI isn’t smooth, but its way better than it was.

But if I try to load in Reason Intro rack into Cubase it hangs. Yet I can load that into heavier more CPU intense projects fine.

Do project files become corrupt ? The audio is fine, there is nothing messed up in the tracks.

Completely baffled here.