Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello Pitschi Florian,
I would like to inform you that, please try to whitelist the below URLs in internet explorer.
https://*.yammer.com
https://*.assests-yammer.com
https:// *.yammerusercontent.com
1. Open Internet explorer
2. Click on settings gear icon
3. Click on Internet options
4. Click on Security
5. Select Trusted sites
6. Click on Sites
7. Add above 3 URLs one by one
Once the URLs are added in trusted sites, then please try to access Yammer from internet explorer and check the behavior.