Porting a world from Version 1.12.2 and having water surrounded by stairs marks the sides of the water blocks (water source) invisible, although the water is there
Update: removing one water source via block placement then removing said block makes the sides of the water sources pointing to that block makes them visible again, but doesn't update any other water blocks
Update 2: fluids surrounded by stairs loses their sides, regardless of water or lava. (Picture below)
See MC-131267