blank EndNote Registration Window

I have upgraded from X9.3 (latest version) to 20.1. MacBook BigSur 11.6 Intel

Every time I open the application, I get a blank “EndNote Registration” window, with two buttons at the bottom “Cancel” and “Sync”… When I click on Sync, it synchronises with the cloud without any problems.

Every time I synchronise, the window appears.

With the right button the “Reload” option appears… but it doesn’t load the content of the window.

Restarting does not solve the problem.

How can I stop the window appearing repeatedly?