I see the baseline is less than 200k monthly unique devices and there
were no huge drops:
https://analytics.wikimedia.org/dashboards/vital-signs/#projects=igwiki/met…
Absent trivial errors, such misclassifications of entire countries have
been caused in the past by ISP changes. (I think the biggest case was
Australia at some point, it was in Erik Zachte's blog.) Things like
moving large IP ranges or slices of traffic from one operator to
another. If I remember correctly, some big internet exchanges have been
built recently in Central Africa, which may have prompted changes.
I'm not sure at what rate the GeoIP information is updated.
Federico