clarification, you want to merge these 2 activities because? The data is different or are they the same just duplicate cos coming from 2 diff devices or from 2 sources ? (eg: Strava + Garmin)
If it’s duplicate, just delete one. if merge - this feature not available (posssibly YET)
Can you determine what these 2 entries sources are from?
YOu can see them on the actual activity, at the top right corner. eg: ~view in Garmin Connect ~ Strava " or something liek that.
Yes unfortunately there are still some race conditions when activities from Strava and another source arrive at approximately the same time that causes the delete of the Strava activity to fail. Manually doing “reprocess file” on the non-Strava one should sort it out.