I got a few villagers, set some trades i wanted, then went afk overnight so my sugarcane farm would generate enough to get a bunch of books.
woke up to this(the attachment). I looked through their nbt with /data, and aside from them having no gossip and the demand being -211999998 theres nothing out of the ordinary.
i messed with their nbt, and found the demand to be the culprit. I watched it for a little bit and it just seems to keep decreasing, and thus rising the price the longer they exist.
I haven't tested in previous versions, but ive never ran into this problem before so I'd assume its exclusive to 1.16.1.