What was wrong
The Ideas section landed a few minutes after the Common Data Set plans and the document-reading agent were finished and left the roadmap. Three ideas (colleges that would compete for you, cycle watch, and getting into the major) still listed those plans under "builds on", and the check that every such link points at a live roadmap page failed. Nothing on the site was wrong; the check caught a stale reference.
What changed
Each of the three ideas now lists only the plans still in progress (where you stand, following colleges, the student profile). The finished work they also rely on is noted in the registry for the day they are built.