When a villager is converted to a zombie villager several times the prices also go down several times, however after trading with them a few times (sometimes it takes quite a lot of trades) the price will go up again temporarily, the price resets to the proper value at the start of the next workday.
For example:
A librarian is converted 4 times and sells 1 paper for 1 emerald, after using this trade several times the trade will go back up to 18/19 paper for 1 emerald as if the villager was converted only once. At the start of the next villager work day the trade will go back down to 1 paper for 1 emerald
Not tested on 1.15 but it probably works the same way
Linked issues
Comments 2
Thank you for your report!
We're actually already tracking this issue in MC-146373, so I resolved and linked this ticket as a duplicate.
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I believe this is working as intended. Trading gossip goes to the "trading" TAG count, which increases prices but goes back to normal over time, so price increase is temporal. Being cured from Zombie goes to "major positive" TAG, which is permanent. So in your case, prices are coming back to normal, and since your villagers were cured several times (5 being the most times with an effect in the game FYI) it's a low price