Steps to Reproduce:
1. Build a water chamber (Easier to add soul sand or magma block for bubble column testing)
2. Try to spawn a IRON GOLEM using 3 blocks of iron and 1 pumpkin or WITHER using 3 soul sands and 3 wither skeleton heads.

Observed Results:
Nothing happen. Both Iron Golem and Wither are failed to be spawned underwater (Both water and bubble column state) using plus-grid-like formation and pumpkin to spawn them in

Expected Results:
Iron golem and Wither should be spawned

P/S: Snow golem can still be spawned underwater and bubble column. It seems like this only affected IRON GOLEM and Wither only.