Today we detected that the page_fans Facebook Insights metric returns for Market Pages in a Global Page structure the fan count of the Global Page, not the fan count of the Market Page, starting from today 23rd Oct, 2018.
We have filed a bug report at Facebooks Bug tracker: https://developers.facebook.com/support/bugs/199640960933157/?disable_redirect=0
As soon as we will get more information we will update this incident.
Note that we also announced the removal of the deprecated fans_local field on the Facebook data source for today. This is just a coincidence and not related with the forementioned case.