'BMW Nav VI' and Joining Tracks?

Hi all.  

This question is for Basecamp (Version 4.8.12 (4.8.12)) on Mac Catalina (10.15.7).  The GPS unit is a rebranded Garmin, called BMW Nav VI.  

I went for a 100 mile ride on my motorcycle, stopping several times to take photos, eat etc.   When I got back and hooked the Nav VI up to my Mac, I see about nine or ten different tracks with today's date.  I select them all, right click and join them.  And then I get this....

Which is the new 'track' containing all of today's?  When I select each of them in turn, none of them has the complete day.  There are some that are seven miles, some that are 70.  But no one track seems to contain the entire ride.

Help!