Compare the hitbox of a slime in Minecraft 1.20.4 versus Minecraft snapshot 24w03b:

/execute align xyz run summon slime ~ ~ ~35 {Size:128,Tags:["MC-267966"],NoAI:1b}

The slime is slightly smaller (about 1/4 of a block) in the snapshot, which seems like an unintended change as it can cause the slime to act differently in some situations.

This issue also affects magma cubes.