Gitlab 18.5 wrong updatetime on groupoverview / No activity

Hello there,
we upgraded to 15.8.0 CE. Now we are facing problems, that there are wrong updatetimes on the Groupoverview. If you go the the dashboard, all times are fine. When you are creating a new project, all times are fine too.
Also if you have a look on the activities, there we are facing the same issue. Activities from new projects are getting listed in the activity-tab, but activities from old projects doesn’t get listed.

Do you know how to fix this?

Sincerely FallingSky