I have the answer. After migrating from 8.0 Update-5 to 8.0 Update-7 (SP1) I noticed that media library items with a space AND a hyphen in the name were returning 404. It has to do with our configuration where we allow items to be created with this (admittedly bad) naming scheme. It seems that the Analytics Dashboard isn't immune to this issue so I had to rename the Dashboard page.
The item is in the Core database, namely:
/sitecore/client/Applications/ExperienceAnalytics/Dashboard/Acquisition/Keywords/Organic non branded
Rename the item key to omit the dash.