Recently just updated game to 1.19 and am now unable to place slabs on the upper-half of blocks. If you try you place them on the lower-half then the next one will place on the upper-half 1 block out. Even if you place a slab on top of the block then go out from it to try and place the slab it will avoid the upper-half completely.

As you can see in the attached image, my cross-hair is on the top slab, but I'm unable to fill the gap with a slab but can place the slabs on below where I'm clicking.