Three possible causes, none mutually exclusive...
1) An illiterate AI picture recognizer saw the swastikas, and presumed the worst thereafter. FB surely doesn't have the labor budget to review very many of these.
2) Perhaps contemporary crypto-nazis are exploiting these defective post-flagging algorithms, spitefully steering them in the opposite direction of their designers intent.
3) Malice, or virtual malice by way of greed-driven reckless negligence, on FB's part.