SImultaneous C6 and SX open - UAD-1 access problems

Seems like if the UAD-1s are being used in one project, they’re not always available in the second one.

I had them both open simultaneously to bring VST connections across to C6. But I could also see if one were bringing a new project into C6 from another version that both might need to be open.

Does anyone’s workflow more than rarely have two instances of Cubase open (C6 and earlier version)? Have you noted any problems like this, or otherwise?