The way the Most Recent Activity column on Find Cases is calculated makes no sense
It shares code with the Case Dashboard, where the Most Recent Activity column only appears in a section for cases that have recent activity. But on Find Cases depending on your search criteria it will of course include cases that do not have recent activity. For those cases, the column displays blank, when it really should simply display the most recent activity, whenever it was.
To reproduce, create a case and complete an activity. Wait 2 weeks. Then do a find cases and look at the Most Recent Activity column for that case.
Does Find Cases even need this column?