They are using Office 365. I noticed the same thing, no other issues with other clients on various hosting and email systems.
It’s occurring on quite a few sites, some of which are just running Wordfence out of the box with no changes really, some have the wp login hidden along with minor changes, and some are more extensive changes. I have tried running a backup while logged in and it gives me the same error as it does when the automated backup fails. When it failed during my manual attempts, Wordfence didn’t show any blocked IPs.
None of the sites having an issue are using Cloudflare or any similar service.
I checked and some of the sites that are incurring this issue have 0 IPs blocked. I verified that on sites that do have IPs blocked, the server IP is not included in the list.
