Update - it looks like whichever site is being cached last is the one being displayed.

So the cache refresh plan has Sites 1-3 being created at 5 minute intervals, but when I run the report the data for site 3 is being displayed, no matter what site I select in the report criteria.

I've never seen this behaviour before - it's almost like the cache is being over-written every time rather than a new version being created.

Any-one got any ideas??