I have a webserver on digitalocean which hosts 3 wordpress instances on one node. The mysql backend is DigitalOcean managed mysql. Two of the websites work fine, but one has an error:

Warning: mysqli_real_connect(): (HY000/2002): Connection refused in /var/www/html/redacted/wp-includes/wp-db.php on line 1653

Connection refused

The wordpress installations are identical, apart from the database configuration. I can login to the database perfectly fine with the credentials that I use in wp-config.php, but the site just keeps giving me this error.

I tried making a new mysql user for it, tried the public mysql url instead of the the private I usually use; nothing works. Everything points to the fact that it should be working, but it just doesn’t. This site has worked before in the past (running since May) and I have no idea when it stopped working, but probably a few days ago.