A linear track is added to the route

Exactly what tmk2 said

I did many others hikes after 03/16/2020.

Then you're not doing it correctly. Try on your next hike. Wait until your gps shows you where you are. Now clear the track log. When you finish save the track.  Now you won't get any straight lines.

This isn't an Express issue though so I'm moving this thread to the BaseCamp forum.

Yes I never controlled if my gps showed where I was. I will do it now.
Thanks.

Those long linear tracks are usually due to a single point at the start or end of the track.  You can remove the point in the track properties window or use the eraser tool on the map (it will but a red "X" on the point that will be deleted).

Devices store their last location to speed up acquisition of satellites.  This location can end up in the track log.

If you are interested in the summary data, it is best to have your device on for 10-15 minutes prior you start.  The reason for this is that the device needs to download orbital data from each satellite in view.

As already mentioned clear the track log at the start and save at the end,  When you download, the summary data will be based on the trip computer and not the stored track.  You can delete one point anywhere in the track to force a recalculation based on the logged track.   Duplicate one of your tracks in BaseCamp and delete a point to see its affect.

A very clear and interesting answer.

Thank you very much.

Following the last instructions it has been possible to delete the straight lines on Base Camp of two routes already saved with this problem.
It works fine.
Thanks again.

And you can avoid them in future so all should be good