I have the same problem and I think this is a bug (shame that none of Garmin reps actually answered OPs question).
The elevation screen behavior is inconsistent between subsequent uses. Sometimes it shows the dot in the 25% from the left (each section on X being 500m so it's showing 500m back and 1500m in advance), sometimes (despite loaded and followed track) the dot is at 75% (more to the right) but most often the dot is not there at all.
Garmin, I beg you, please fix this issue, it makes elevation screen useless.