So, we figured out what it was.
In the options
table (wp_options
for some, we chose to do away with the wp
prefix), there’s a user_roles
(or wp_user_roles
value). One of the plugins we used (Yoast SEO in this case) had an update that zapped the value of that option, removing the Administrator role from that list. As a result, no admin could log into the admin panel. Once we restored that particular row to its former self — things started working again.