EndNote 8.1 seriously slow on MacOS 10.13

Just got off the phone with tech support. 

THEY SOLVED MY PROBLEM. 

Apparently, if you have PDFs in your database that CONTAIN ANNOTATIONS, this is causing the problem. 

I only had two PDFs.

When I removed them, problem solved. 

They are taking the issue up with Apple and are aware of it. 

In the meantime, delete your PDFs and it should help