That happens quite often because owner of directories under Wordpress has been changed to root. If that’s true then chown -R www-data:www-data /var/www/public_html or similar depending of distro and paths helps.
Yeah, in the most of cases poor admin sees that issue every time when month has changed and tries upload media.
I’ve got same error with other plugins, but not recently. But I can’t remember what was the issue then — but I have very weak memory image of badly behaving origin of plugin. Or I did some funny things with geo-ip and/or blocking IPs.
Do you use any security plugins? Or Fail2ban?
WP-CLI could give a bit more informative error. Or not.