If any Facebook Page administrators were wondering about iffy reach and engagement metrics for posts recently, Facebook quietly provided an explanation today.
As reported first by the Inside Facebook blog, Page managers who access the Insights dashboard are seeing this message:
There is a discrepancy in the engagement and reach metrics for all Page Posts and Boosted Posts between 5/30 and 6/30. We are working to resolve the issue as soon as possible.
I have reached out to Facebook for more information and will update if I learn anything new.