there was a glitch for a while – but the newest updates, I thought fixed it. what Endnote and version are you using? The work around used to be to increase the number by one, I think in your output style.
added in edited comment
but maybe it is still there according to this thread. I do agree with one commenter. Usually the rule is not applied if there is only one more author. Problematic bug/error in EndNote 20.0.1 - Wrong number of authors in some styles