(it would be great if you could choose “options” from the other duplicate posts, and delete them, but that might not be possible, if they were each “replied” to.)
Below is slightly modified from
Make certain that all author names are consistently entered into your _EndNote _library, including spacing and punctuation.
With regard to the author firstname issue.
"For example, if you have entered
as an author in one record, "
(edited to add)
and Smith, John
or Smith, J. A. in another record
“you need to make sure every other instance of that author’s name in that library is identically formatted” (Edited: and best to do this by copy and paste). “Please note that a difference as small as one space may cause _EndNote _to believe it is dealing with two separate authors and add the initials.”
This is because APA requires disambiguating different authors of the same surname in citations, and Endnote is not clear if J Smith is the same author as John Smith.
That article starts with changing the style to remove this feature, but if it were John Smith and James Smith, then you would want the citation to so designate these - to conform with APA requirements.
Second. Is the difference whether it is the first time cited in the text vs a subsequent citation of the same reference in the text? APA has two settings as shown in the attached image. If you want them treated the same, you will need to edit this setting, “save as” and then ensure that your endnote output style is changed to the new version (do not use the same name) which the first time you want to use it, may not show up in the dropdown list, and you may have to “select another style” and select the newly edited output style you just created. From then on, it should show up in the drop down.