I cured a mending villager and it started selling a mending book from 26 to 1 emerald. I bought a few books (around 15 mending books) and then it went out of stock.

After a while I checked and it had replenished it’s stock, and the price was still 1 emerald.

After another while, I checked and it went from 1 emerald to 2, even though I didn’t trade anything new with him (and I didn’t harm him or any other villager either)

After another while I checked again and it went from 2 to 6 emeralds, and now it seems to be stuck in this price.

Why did it increase so much? I tried zombifing and curing him again and it’s still in 6 emeralds.