Not saying this is anything, but maybe someone else on here will see this and have a lightbulb moment...
All 3 DNS records for Facebook, Whatsapp and Instagram were updated on Sep 22.
https://whois.domaintools.com/facebook.com
https://whois.domaintools.com/whatsapp.com
https://whois.domaintools.com/instagram.com
I also noticed the same date on the other domains:
https://whois.domaintools.com/whatsapp.net
https://whois.domaintools.com/facebook.net
I am sure there are others. This could be just a simple Zuckerberg and Co. had something they changed/updated on that date for the entire FB empire, but I find a massive outage a few days (12) later to be really strange.
I do not have a whois premium account so I am unable to dig much further than this. Anything interesting happen on Sep 22?
https://blog.cloudflare.com/rpki/