==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):
1.6.6 MariaDB Edition
- Deployed with iRedMail Easy or the downloadable installer?
Downloadable Installer
- Linux/BSD distribution name and version:
Debian 10 Buster
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
MySQL
- Web server (Apache or Nginx):
Nginx
- Manage mail accounts with iRedAdmin-Pro?
Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Hi, since the Upgrade from roundcube 1.5 to 1.6.4 we expiriencing an performance issue in the roundcube webmail. Sometimes when we switch folders or subfolders the session gets stuck and in the right lower corner an error message appears "server connection failed". after like 20 seconds the session is restored. We also get this error when we move mails into subfolders etc. Sometimes we get an gateways error from the nginx and need to reload the site.

the only error log we can find is in the nginx/error.log:

upstream timed out (110: Connection timed out) while reading response header from upstream, client: 62.178.XXX.XXX, server: _, request: "POST /mail/?_task=mail&_action=refresh HTTP/2.0", upstream: "fastcgi://127.0.0.1:9999", host: "mail.example.com", referrer: "httpx://mail.example.com/mail/?_task=mail&_mbox=INBOX"

Roundcube Version 1.6.4 with PHP 8.0 cli and fpm