Cannot place slab under existing slab

When placing a lower slab, I cannot place a slab under it. It always places a slab below it meaning it skips a slap. No matter how I try to place it, upper slab, lower slab, I will not place on the e dusting slab.  This is on either pocket edition running current iOS and current MC edition or PlayStation 4 and 5 running current software and current Minecraft edition. Already searched the database for resolutions and there are none that effect the current situation.