TLDR: If you are using a Xiaomi phone like the Mi 4 or redmi series then:
- Go to the Whatsapp site and download and install the apk (you may need to enable third party app installs in settings)
- Disable auto updates on the Mi app store to prevent similar issues with other apps
On opening Whatsapp yesterday (13 Jan), I was greeted by a message saying that the version of Whatsapp was obsolete and had expired on that day. Oddly, there was no update available on the Google Play store and I was not on their beta testing program either.
A bit of searching seemed to indicate that this was a MIUI problem, in particular due to their Mi App Store which seemed to be updating apps automatically. There was however no app update on it either.
Finally read on the discussion thread that downloading the apk directly from the Whatsapp site fixed the problem for most and that was exactly what I did. I also went and disabled the Mi app store auto updates to ensure that other apps don’t end up this way.