Looks like their auth DNS dropped out of the DFZ:

https://twitter.com/g_bonfiglio/status/1445056923309649926?s=20
https://twitter.com/g_bonfiglio/status/1445058771261313046?s=20


-- 
Hugo Slabbert


On Mon, Oct 4, 2021 at 9:21 AM George Metz <george.metz@gmail.com> wrote:
Also impacting Instagram and, apparently, WhatsApp.

On Mon, Oct 4, 2021 at 12:05 PM Eric Kuhnke <eric.kuhnke@gmail.com> wrote:
>
> https://downdetector.com/status/facebook/
>
> Normally not worth mentioning random $service having an outage here, but this will undoubtedly generate a large volume of customer service calls.
>
> Appears to be failure in DNS resolution.
>