Structures in 20w21a no longer spawns mobs

Since the fix MC-184740, structures no longer generate mobs as of 20w21a. This will affect some speedrunners who play at the snapshot. The bastion in the screenshot no longer has Piglins and only has Magma cubes and Endermen (the bastion is generated in a warped forest)

A solution to this would be to convert structure tags from the old format to the new format upon loading world.