I can’t reproduce it, because your activities are private. That’s ok - no need to change your privacy settings!
Does it work properly if you visit the beta ( Beta: LifeMap performance )? https://citystrides.com/users/12066/map_beta
If it does work properly - do you see a square with an X through it here? https://citystrides.com/users/12066/map_beta#-4.956964933525512,-4.319127608810504&4.464277395631693
If you don’t see the square/X, then the issue is probably that you’re running too much. Have you considered sitting on a couch, or if this is an extreme case, just staying in bed? 
But really, the map does fall apart after a certain amount of data is added to it - which is why I’m working on the beta. I want to check with the Mapbox team about this, though, because they claim to support handling large amounts of data and I don’t think any of us are throwing that much at the map 
maybe we are.