New users not showing up in Post -> Edit

s_ha_dum’s answer prompted me to look into this a little further. I checked the users in the database. It turns out that the dropdown list in Posts -> Edit is using the Display Name, not the User Login, as I had expected. So, the problem was not that WordPress was functioning incorrectly, but that my understanding of what field was being used was incorrect. I guess this was a “false negative.”

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)