It's the entirety of North America, parts of South America and Africa completely blacked out until April 15 - no reward seats at all in any cabin. Availability then improves sharply on April 15. Seats in F are scarce in those affected destinations, but that's normal because F tends to show up days before. But on the flip side, there are certain cities that appear to have an abundance of F one way (not both) outside of the blacked out regions.