The game tries to spawn bogged without experimental feature "update 1.21" active (but failed)

The game tries to spawn bogged (failed) without experimental feature "update 1.21" active.

Step to reproduce:

1.Create a non-experimental world in 1.20.5 pre1.

2.Locate biome "Swamp".

3.Wait for a while and see the output log.

Observed result:

.You will found"[Server thread/WARN]: Can't spawn entity of type: minecraft:bogged" in it.

Expected result:

The game won't try to spawn boggeds.