I’ve experienced this as well, but before 1.17 (though I don’t know the version). I also just had this happen in 1.17.1. I cured a fletcher four times and on the fourth, instead of going all the way down to one stick for an emerald, it went back up to 26. Which is equivalent to curing it once. So I basically wasted 3 golden apples and potions (which aren’t to hard to get) but it is frustrating. I checked out the linked bug the mod posted, but it isn’t the same thing. I do think this is a bug, not intentional.
I’ve experienced this as well, but before 1.17 (though I don’t know the version). I also just had this happen in 1.17.1. I cured a fletcher four times and on the fourth, instead of going all the way down to one stick for an emerald, it went back up to 26. Which is equivalent to curing it once. So I basically wasted 3 golden apples and potions (which aren’t to hard to get) but it is frustrating. I checked out the linked bug the mod posted, but it isn’t the same thing. I do think this is a bug, not intentional.