You would first want to determine if the issue is document specific.
If you try inserting into a new blank Word document do you get the same behavior?
If it only happens with a certain document then try the steps at:
If it happens with a new blank Word document then please contact Technical Support directly:
1-800-336-4474 option 4 then 1
or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US
We are here to help whenever you run into issues.