Some reference standards abbreviate journal names. This applies to Vancouver, among others.
The journal: Journal of Cancer Science & Therapy
Abbreviated: J Cancer Sci Ther
The journal: Journal of the American Society for Information Science
Abbreviated: J Am Soc Inf Sci
Title abbreviations are controlled by journal abbreviation lists, which must be imported, in Endnote.
In the pop-up window I select "Journals" and click "Import List..."
Mac: You must find the folder where you have installed Endnote: Hard disk/Applications/EndNote (EndNote version number)/Terms
Select the list that fits your subject area and open it.
It is possible to import multiple lists. But they must be imported one at a time.
Read more on Clarivate Analytics, including how to delete incorrect abbreviations: https://support.clarivate.com/Endnote/s/article/EndNote-Generate-full-or-abbreviated-journal-names?language=en_US