I’m glad you have found what is creating your long startup issue and the association with your UAD plug-ins. Now is the much tougher task to find the root cause.
This link below lists several suggestions. Every one will probably help a little. From just running the eLCC maintenence to changing the USB dongle to a newer version to, as you mentioned, exclude some folders from antivirus. Even a few others.
My suggestion would be to do the easiest suggestions first and cross your fingers. Also, it can’t do any harm to submit a support ticket to Steinberg through your MySteinberg account. And yes, your idea about posting on the UAD forum too.
Good luck. 
Regards. 