Box with LR works for me. Can you provide an example file? Otherwise it's hard to say anything useful.
Theres one for today I could send you, but dont know how or where to send it
I found out, :-O)
what I had missed was that I should select ALL tracks, the the whole route is shown, after that I selected all photos from that period (day) and used Map/Tracklog/Auto-tag photos, then the photos gets their GPS coordinates
Now that is great... but not too intuitive to use.
If you have to select all tracks manually to show your route on the map display, there is probably something non-standard about the gpx tracks that your app generates. I never have to do that. Lightroom always shows the entire track from the last loaded gpx file and I only have to select all my images and do and auto-tag. I generally use gaia GPS or Motion-X gps.