I think I posted this network here the other day but can't remember for sure so have it again.
Maybe look at blocking 2a0e:d683::/32 at your edge if you support IPv6. I've seen failed logins from thousands upon thousands of IPs in that network in my O365 tenants for a while now. They do a nice slow roll so I generally see each IP less than once per month, but I would suggest looking for successful logins in your tenants from that network and respond accordingly. And maybe look at conditional access policies if you can.






