Stream Items have disappeared from Group Timeline

Hello

I am having several issue with a group timeline.

In my site (dev), go to "Altitudes Paris" group. You will see stream items regarding events in group (event creation etc.). Now click on Timeline in group menu. Stream items for events disappear :-(

Also, when the stream items for events are displayed in the group, not all of them are here. You can see there were several events created in the group, but there are stream items in the group only for the latest event creation ("Soirée Tarot / Belote Garennoise").
And some photos that were posted in the group are not in the stream anymore (you can find these photos in the "Story Photos" album).

All the stream items that have disappeared from the group timeline were displayed some time ago, and I can't figure out why they are gone now...

Thanks