In 1.21.10.21 Preview changelog said:

"stone_block_slab4" block is now split into unique instances "mossy_stone_brick_slab", "smooth_quartz_slab", "normal_stone_slab", "cut_sandstone_slab" and "cut_red_sandstone_slab"

However, Stone Slab using incorrect block ID. This is causing existing stone_slab ID does not change to the correct block currently (using /give @s stone_slab gives Smooth Stone Slab)