Gadget titles showing as __MSG_gadget

[Kristronics GmbH]

Hello folks,

we have a problem with our jira-software instance. Most, (but not all) gadget titles show as __MSG_gadget... I followed the steps mentioned here: fix gadget titles 

I put my answers next to the step in bold text

• iptables or firewalld has been configured to forward packets from 80 to 8080 and/or 443 to 8443 We don't use iptables or firewalld
  
• From the Jira server itself, Jira is unable to communicate with itself via its Base URL (Run curl -v <base_url> to verify) curl works!
• Run SSLPoke from the Jira server itself and see if it returns successfully SSLPoke returned "successful"
• Additionally run the httpclienttest from the Jira server itself to confirm if the SSL configuration is okay, as this will verify if you're affected by  JRASERVER-47568 - Spurious SSL SNI errors in Jira server 7.0.2 Closed httpclienttest successful
• There are application links configured in Jira but they seem to be having some issue we have no application links, all deleted
  
• Outbound proxy is configured and Base URL is not whitelisted no outbound proxy
  
• Using a plugin to prevent anonymous access no such plugin
  
• Reverse proxy information is missing from the HTTP connector when using a HTTP proxy we use a https reverse proxy
  
• When using an AJP connector, there's no retry element in the ProxyPass directive at the proxy server no AJP Connector
  

The Jira-Server is behind a apache reverse proxy with ssl configured. The certificate (wildcard from a trusted CA) is imported into the keystore.

The server can reach itself, I also tried to add 127.0.0.1 jira.ourCompany.com

to the hosts file but it doesn't change anything.

Is there any way to test, where the problem is? I have no idea what to do next.

OS is Win Server 2k16 64Bit

Jira Version 8.9.0

Thanks for your help

Best regards