==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.7 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer? Installer
- Linux/BSD distribution name and version: Ubuntu 20.04.3 LTS
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MYSQL, I think.
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? PRO
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Performance issues in webmail since updates. Accessing inbox, it is loading for a long time or says refreshing. Sometimes completes, sometimes times out and then get Server Error Gateway timeout.

I updated:
iredmail from 1.5.1 to 1.6.7 incrementally one version at a time.
iredadmin to 2.5
mlmmjadmin to 3.1.9
netdata to 1.34.1
iredapd to 5.3.3
Roundcube to 1.6.5
I updated iredadmin-pro directly from 5.0 to 5.6 (not incrementally)
Nothing else was updated yet.
I plan on updating Ubuntu next.

What error logs should I check?
Any suggestions?