WhatsApp, broken on Windows Phone 8.1 and with no immediate fix promised, has vanished from the Windows Phone Store. Searches for the app on devices running both Windows Phone 8 and 8.1 turn up "We couldn't find a match. Try a different spelling or search term." WhatsApp tells us that the removal was intentional, though it should only be temporary.

Visiting the app on the Windows Phone Store website turns up the listing, but with the warning that "This app is no longer published", and thus no option to remotely install it.

We don't have a reason for why WhatsApp was pulled - while it was prone to malfunction in Windows Phone 8.1, the app was still fully functional on Windows Phone 8. It's possible, knowing that Windows Phone 8.1's release was imminent and that their app would offer a less than satisfactory experience as a result, WhatsApp opted to remove the app until they get it updated. It's better to not be there at all than to leave users with a sour taste in their mouths.

WhatsApp has informed us that the removal of their app from the Windows Phone Store was an intentional one, taken to address technical issues. Those that have downloaded the app should expect it to continue to work for now, but until WhatsApp has finished "working closely with Microsoft to resolve the issues", we wouldn't expect to see the app returned to the store for download. That WhatsApp chose to pull the app entirely is some indication that there was some serious showstopping bug or other issue that they couldn't allow to go on, though they've been unclear as to what exactly that might be:

Unfortunately due to technical issues, we have chosen to un-publish WhatsApp Messenger on the Windows Phone platform. We are working closely with Microsoft to resolve the issues and hope to return to the store shortly. We apologize to our users for the temporary inconvenience