==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.2.1 MARIADB edition
- Deployed with iRedMail Easy or the downloadable installer? Downloadable
- Linux/BSD distribution name and version: CentOS Linux release 8.2.2004 (Core)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginix
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Brand new install of iRedMail. Logging in to Roundcube with default admin account created on installation.

I get yellow box on bottom left saying "Connection to storage server failed"

Seems that this boils down to this in the /var/log/dovecot/imap.log:

Jun 24 12:17:14 almtrd dovecot[8722]: imap-login: Login: user=<postmaster@alarmtraders.com>, method=LOGIN, rip=127.0.0.1, lip=127.0.0.1, mpid=8807, secured, session=<ZVgWz9aoGph/AAAB>
Jun 24 12:17:14 almtrd dovecot[8722]: imap(postmaster@alarmtraders.com): Error: Plugin 'imap_stats' not found from directory /usr/lib64/dovecot

I apologize if this is an FAQ, but searching did not turn up a match for me.