MC-227064 – Floating grass can still generate above water lakes.
MC-229365 – Large amounts of goats cause performance issues.
From the development versions
MC-236617 – Mountains and gravelly mountains use their 1.17.1 biome ID name.
MC-236632 – Banners without patterns do not render properly.
MC-236663 – Command blocks do not display command in their UI.
MC-236736 – No relief on treasure map or explorer maps.
MC-236896 – Strange mini broken aquifer walls generating commonly on the surface.
MC-237490 – The bottom parts of aquifers aren't always surrounded by blocks which can occasionally cause them to spill into caves in ways that appear bizarre.
MC-237666 – Unused biomes still present in game files.
From the previous development version
MC-237925 – Opening world from 1.12.2 (or older) in latest snapshot regenerates random chunks.
MC-237933 – Sweet Berries generate much too often.
MC-237950 – Cave vines can generate without tip because prioritize_tip option is negated.
MC-169532 – As of 18w06a, the sand, clay and gravel blocks no longer generate around small lakes.
MC-175929 – Ice spikes get cut off below height limit on AMPLIFIED worlds.
MC-182362 – Score callbacks with a too long name break callback chain.
MC-183184 – Sprinting stops as soon as you touch another block.
MC-186042 – Plains biome is always generated when a swamp borders a desert, snowy tundra or snowy taiga.
MC-188096 – Gravelly mountains+ is no different than gravelly mountains.
MC-190363 – Some biomes generate as "Single biome" worlds in "Floating islands" world type.
MC-193348 – Status effect bars shift the player's inventory in Creative mode.
MC-196723 – If the player gets an effect in Creative mode while their inventory is open and not having an effect before, they won’t see the effect in their inventory until they close and open their inventory.