Many of these companies have taken the (true) statement that the company's insured depository accounts at various banking institutions are FDIC insured and presented it to customers in a misleading way, and the FDIC wants them to cut it out. The FDIC also demanded websites who published statements like "Is CEX.io Safe? Yes, Cex.io is a safe crypto exchange. Actually, one of the safest on the market since they are FDIC insured..." take them down.
CEX.io is a London-based cryptocurrency exchange with comparatively low trading volume compared to its larger competitors like Binance or Coinbase.