The issue could be the way you have the Authors entered.
I would make sure you have the authors entered one name per line.
Please see the following KB articles on this type of issue.
If this does not resolve the issue 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