==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):
- Deployed with iRedMail Easy or the downloadable installer?
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
- iRedMail version 1.4.1 MARIADB Version
- deployed manually ("wget ... from IredMail")
- running on Ubuntu 18.04
- Mails stored in MARIA DB?
- Web Server Nginx
- No iRedAdmin-Pro

After upgrading SOGO to Version 5.5.1, I was unable to login again.
I followed this instructions to deal with the Proxy Buffer issues as this seems to be a known issue.
So, I added the
proxy_busy_buffers_size   64k;
proxy_buffers             8 64k;
proxy_buffer_size         64k;
Into the sogo.tmpl file as instructed.
This worked in the sense that after I modified the sogo.tmpl file, I could login to Sogo again.
But now there is a new issue, occuring estimated 1 - 2 minutes after successful login.
I get an "Internal Server error" in the right bottom corner.

The /var/log/sogo/sogo.log shows the following (sample only)
Apr 22 12:56:11 sogod [1037]: |SOGo| request took 0.171019 seconds to executeApr 22 12:56:11 sogod [1040]: |SOGo| request took 0.170385 seconds to execute

Apr 22 12:56:11 sogod [1037]: 10.120.40.96 "POST /SOGo/so/gmx@office.local/Mail/0/folderINBOX/changes HTTP/1.0" 200 26/150 0.174 - - 0 - 15
Apr 22 12:56:11 sogod [1040]: 10.120.40.96 "POST /SOGo/so/gmx@office.local/Mail/0/folderINBOX/changes HTTP/1.0" 200 26/69 0.174 - - 0 - 18
Apr 22 12:56:24 sogod [1037]: |SOGo| starting method 'POST' on uri '/SOGo/so/gmx@office.local/Mail/unseenCount'
Apr 22 12:56:24 sogod [1037]: |SOGo| request took 0.017980 seconds to execute
Apr 22 12:56:24 sogod [1037]: 10.120.40.96 "POST /SOGo/so/gmx@office.local/Mail/unseenCount HTTP/1.0" 500 36/258 0.021 - - 0 - 16
Apr 22 12:56:25 sogod [989]: [WARN] <0x0x55ac1403c730[WOWatchDogChild]> pid 1036 has been hanging in the same request for 2 minutes
Apr 22 12:56:26 sogod [1036]: <0x0x55ac1448a350[SOGoActiveSyncDispatcher]> Sleeping 30 seconds while detecting changes for user heinrichp@office.local in Ping...
Apr 22 12:56:26 sogod [989]: [WARN] <0x0x55ac140e0890[WOWatchDogChild]> pid 1051 has been hanging in the same request for 2 minutes
Apr 22 12:56:27 sogod [1051]: <0x0x55ac146fc210[SOGoActiveSyncDispatcher]> Sleeping 30 seconds while detecting changes for user gmx@office.local in Ping...
Apr 22 12:56:50 sogod [1037]: |SOGo| starting method 'POST' on uri '/SOGo/so/gmx@office.local/Mail/0/folderINBOX/folder_2017/view'

So, from what I understand, the request returns "500" where it used to return "200" before the error.

After this error occurs, I cannot load any eMail in SoGo Frontend.

When I logoff and login again, it works again for some minutes.

Mails are coming in / getting out correctly.

I have only limited knowledge of Sogo, so maybe I am looking in the wrong logs?
Please advise how to narrow down the issue.

I have attached the error message, knowing that it might be of limited help only.

Thanks!