Mjøsa relation was broken, see comment here. Tickets about similar incidents in the past (e.g. T159977) suggest that there isn't much that users themselves can do about fixing this on Wikimedia maps.

At the very least there should be an easy-to-find documentation on how to report such incidents so that they would get fixed reasonably quickly. On openstreetmap.org users can submit individual tiles for regeneration by adding /dirty at the end of tile address. Would it be an option to add similar functionality here? We shouldn't wait for Wikimedia's next monthly update of zoom levels 0–9 in situations like this, especially in more dreadful cases of vandalism.

I don't know the pros and cons for updating monthly vs something shorter, but unless daily or shorter is workable I think some availability for (some?) users to mark dirty some location should be done.
Although not discovering such comments as "Burma is no longer underwater." would be a loss.

Mentioned in SAL (#wikimedia-operations) [2019-09-02T17:57:14Z] <mateusbs17> regenerating tiles from z0 to z9 in eqiad and codfw- T231691, T230511