With your EndNote library open, I’d suggest clicking Tools>Library Summary… to confirm the “Location:” information shown here - is your library stored on your local hard drive, or a network drive / external drive?
Is your user account perhaps re-directed to a server location? What happens if you close your library and open the Sample Library from the “C:\Users\Public\Documents\EndNote\Examples” folder? Do you have the same issue with this library?
Update Java from Java.com ! WOW! FINALLY got something to work! FYI, Running OSX 10.14.16. Endnote 8.2. Now it is fast again! FYI IU shut down endnote while I installed Java to ensure some issue wouldn’t crop up. Then simply booted Endnote again without reboot of computer.
Boom! Thank you to ScrippsOcean. No thanks to EndNote for not helping other than simply having the forum (some help).