I'm uncertain since when it is like this, might be since 2.7.0, or earlier:
I recall the countries on the map being coloured according to how many visits/actions/whatever they have. In blue, like this:
However, it currently looks like this:
Has the design been changed or is this a bug?
(While gathering information for https://github.com/piwik/piwik/issues/6289, I also noticed that the tooltips only work on non-highlighted countries. No tooltip shows for the highlighted ones.)
There is an error "undefined is not a function" below the map, so indeed
this is a bug. What is the full error message?
What browser do you use?
Maybe try to delete files in tmp/assets/* and try again?