Villagers wont breed into Swamp Traders in the experimental Villager Rebalance

Bring 2 villagers from a plain village into a swamp, place 3 beds and give 12 carrots to each villager so they breed. The expected situation will be a baby swamp villager, however a generic Npc is spawned, and cannot sell a Mending book.

This bug comes from the experimental feature of Villager trades rebalance, in a world created in 1.20.6. The bundle, and 1.21, before updating, experimentations are also on

[3 screenshots]

Thank you very much for your acknowledgement