This has now been resolved, thanks for your patience while we worked through the issue.
The problem was with a single Site24x7 (used by ManageWP) monitoring node being blocked in the US AWS WAF.
Investigating · UTC
We're getting some reports of false positive alerts from WP Manage (Site24x7) to some sites on AWS US East 2. We're investigating the issue and we appreciate your patience while we work out the cause.