I was trading with some villagers in a 1.15.2 Realms server. I traded with the villagers and they did not restock their trades even though the restock sound effect was played (specific trades were: farmer-carrot, toolsmith-iron, weaponsmith-iron). They would not restock until their workstations had been reset multiple times and multiple in game days had passed (unsure what cuased the restock to finally trigger).
After making discounted trades with cured villagers, their prices would randomly raise again. Prices would also go up rather than down after multiple successive trades (once again, carrot and iron trades were the ones I found this on).
Duplicate of MC-146373 and MC-167002, both of which are intentional behaviour and not bugs.