The issue isn’t the length, but that there is likely to be another paper cited with an author with the surname “Li” with different initials. Most publishers’ styles require that two authors with the same name be distinguished from one another by their initials.
Sometimes this happens by mistake, when one record is Li, William and the other Li, W and other times it is truly two different authors, Li, W and Li, R. In the first case you can fix it by copying Li, W to both records. (even spacing and full stops can trick endnote.)
If you truly want to ignore the correct formatting rules, you can change the output style to (inappropriately) cite them without initials.
Hmm… I didn’t realize that the APA style requires initials to be displayed for two authors of same last name.
I tried to change one of the authors name to “Li[space]” and leave another as “Li”.
and it works! Now both were cited as the last name only without initials. Though it’s not the correct APA style, that’s how my lecturer wants it to be.