Facebook is currently facing a bug returning relative Page Like/Fan counts (compared to the day before) instead of the lifetime number of Page Likes / Fans. This only affects private-level Insights data (data source facebookInsights in quintly). This results in very small or even negative numbers to be shown as the private-level Page Like / Fan count in quintly for any Facebook Page for the last few days since January 15th, 2021. We can confirm that the same problem exists in Facebook's own Insights dashboard.
There is already an open bug report tracked at
https://developers.facebook.com/support/bugs/443997473399054/ . We hope Facebook to fix this very soon, so our system can also update historic entries.