==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.9 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer?downloadable installer
- Linux/BSD distribution name and version: Ubuntu 18.04 LTS 4.15.0-55-generic
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginx
- Manage mail accounts with iRedAdmin-Pro?
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

On Sogo and Roundcube, we have issues related with loading imap folders, a look to the sogo log shows imap connections errors,
Aug 07 14:45:48 sogod [2514]: [ERROR] <0x0x55eb73553700[NGImap4Connection]> could not sort contents of URL: imap://postmaster%40mydomain.com@127.0.0.1/INBOX/
Aug 07 14:45:48 sogod [2514]: 172.16.10.231 "POST /SOGo/so/postmaster@mydomain.com/Mail/0/folderINBOX/view HTTP/1.0" 500 72/48 10.028 - - 0

but imap log in dovecot show

Aug  7 21:00:59 iredmail1 dovecot: imap(postmaster@midomain.com): Error: rename(/mnt/mailstore/vmail/vmail1/mydomain.com/p/o/s/postmaster//Maildir/new/1565191067.M685018P47861.iredmail1,S=2022,W=2069, /mnt/mailstore/vmail/vmail1/mydomain.com/p/o/s/postmaster//Maildir/cur/1565191067.M685018P47861.iredmail1,S=2022,W=2069:2,) failed: Invalid argument

We are using shared NFS Storage. I take a look to the permissions and it appears ok