Garmin Instinct - Elevation graphic issue?

Hello there,

I noticed an oddity during my outings in the wild. when I go out I use the tracks created on the garmin site (.gpx) and load the track on the watch so as to have a distance and the complete elevation plan that I see CORRECTLY.

Often, halfway if I view the altimetry it is no longer complete but "flat" and zoomed in preventing me from seeing the complete track altimetry. A mistake or am I not understanding something? Thanks!