Issue
The map preview within a page will sometimes show a blank white box. The full screen button and bottom-right attribution text is still visible. The map renders correctly when the user opens the full screen mode.
How to reproduce
No idea on what causes this, but it will sometimes appear after making an edit to the page that contains the map. The problem persists across different browsers and machines, suggesting it may be a bug on the wiki-side.
Workaround
Make an edit that breaks the Kartographer map (such as delete a parenthesis), then revert. This normally clears the problem. Purging the page doesn't fix: https://en.wikipedia.org/wiki/Wikipedia:Purge