In a hard level game I am currently playing I cured a pair of zombie villagers, made them into farmers and started trading with them. At first they gave me great discounts, but after a few days of play I suddenly noticed that not only had they stopped applying the 'gratitude' discount, they were charging me more than double for the trades relative to farmer villagers that had never been zombified.

This is not related to the issue reported in MC-154504, because no version upgrades were applied.

SPECULATION: between curing the zombie villagers and noticing their changed behaviour new Microsoft accounts were introduced. Could this have changed the player ID in some way?