Similar story. I’m in the middle of watching a movie an and paused it briefly. When I return to continue watching movie, it indicates that I can rent it for $3.99! Further, all of the movies on my watch list , which were free, now require a fee!
De-register your Tv or sign out of Prime, then sign back in. I have Amazon Fire TV, so I de-registered my TV, then re-registered the TV and signed back in to Prime and everything went back to normal ( no charges) for tv shows.