Extremely slow mail opening after migrating from zimbra to carbonio

Hello everyone,
We need your help.
We have migrated our production zimbra to carbonio.
We have a multi-node system, i.e. three servers : a Ldap server, a mta/proxy server and a mailbox server.
The three servers have large resources in terms of cpu and RAM.
We have a lot of trouble opening our mail, on migrated emails, they take a long time to open.
All users are currently complaining and asking for the old zimbra mailbox.
We use an external ldap server to authenticate ourselves.
As system administrator, we receive a lot of complaints from users.
We are on the latest version of carbonio. 24.9