Every month I check to see what’s new at https://trailhead.salesforce.com/quests (which doesn’t seem to update monthly anymore, but randomly following marketing events). Once in a while, I will complete all of the steps of a given quest and it still shows less than 100% complete.
In previous cases, it has been because some module that I had completed in the past had added a new step. So, while that module was complete on my profile, the current version of the module was incomplete. My guess is that the individual steps are reading from my profile and the aggregated score is based on current state. Anyway…I have learned that when the completion status doesn’t match to look at modules that are over a few months old and find the one with the new task.
Today, my tried and true method failed me. Everything was complete, but I still had only 88% complete on the summary. Hmmm. I got lucky and found Community thread with my first query that had the answer (fortunately near the top, as the thread continues with several more comments that are less helpful), which is to click Unfollow, then go through and click all of the “Mark as Complete” buttons again.
Noting this here so I remember for the next time.
HTH
© Scott S. Nelson