Connection to Storage Server Failed, Could not connect to ssl 993 Unknown reason

[3x5]

I know others have asked this question, but their solutions don't seem to work for me. I can send and receive email fine on my mail server, but I can't get into webmail. I'm running webmail on another VPS, and it's working fine. I cloned this VPS and reconfigured it for a different domain, and it worked for a long time, and suddenly it doesn't work.

When I try to log in, I get 'Connection to Storage Server Failed'. When I view the logs, I see

```
IMAP Error: Login failed for [email protected] against americansurvivor.org from 2601:244:0:6bb:a732:a891:f058:faae. Could not connect to ssl://americansurvivor.org:993: Unknown reason in /var/www/roundcube/program/lib/Roundcube/rcube_imap.php on line 200 (POST /?_task=login&_action=login)
```

Both servers use LetsEncrypt, and certificates are valid on this server. the configuration is identical on both servers: config.inc.php, and the conf files for the virtualhosts are virtually identical. I upgraded all packages on both servers, and still, webmail only works on one.

I am at a total loss as to how to resolve this, since I can only reproduce the problem on one server, the configuration from both seems the same, and the error message is so vague. Could someone help me out?