Upcoming Elevation almost completely flat

Following tonight's route, the upcoming elevation graph was constant at 0ft for almost the entire ride, though the hill climb feature continued to work, and the unit correctly recorded the ~2000ft of gain throughout the loop. The upcoming elevation graph did show two spikes shooting instantly up 10K or more, but otherwise was completely useless for tonight's ride.

a) what went wrong? I was following a known, plotted route, and the unit knew where the major climbs were, so it's just the upcoming elevation graph that was broken.

b) how to hide the graph mid-ride? I found I could tap it and get some sort of refresh icon to appear, but otherwise, couldn't find a way to interact with the graph at all.