Hi ​@tubeless,

check your privacy settings - in the mobile app, go to the tab You > tap the gear wheel in the top right corner to open Settings > section Preferences > Privacy controls > Group activities. 

Here's some more information about how it works: 

https://support.strava.com/hc/en-us/articles/216919497-Group-Activities

That looks about right. Have you checked the article I posted? It includes details on which activities do group and which not / how the criteria work… also - if the other athletes disabled the grouping, it wouldn't help if you enable it on your end only.