Hello @Thorkild
So sorry this is happening.
We are currently aware of an issue where some activities may not appear on your personal heatmaps or may appear under the wrong sport type on your heatmaps. While our colleagues work to resolve this situation, I would like to share a workaround which will hopefully solve this for you:
Navigate to the activity on Strava which is not appearing correctly on your personal heatmaps and choose the option to edit the activity. From the Edit Activity page, change the sport type on the activity to any of the available options, save your change, then edit the activity one more time to change the sport type back to the originally selected value.
Performing this action should trigger our system to re-evaluate the activity, appropriately placing the activity on your personal heatmaps.
Please let me know if that resolves the problem and again, apologies for the issue.