I placed water next to a cobblestone stair(which had the water hacked tag)
and I notice that the water became invisible, this issue happens with slabs, when the water is above them, and with stairs when they're upside down and theres a water block adjacant

Evidence and Confirmation of water being there is shown below

However, in other positions, water is shown.

To recreate it, do what i did with the slabs

and for the stairs, you cant make bubbles visible in air, hence theres water