Affects Version/s: CU14/1.17
Affected Platforms:PlayStation 4
1) Stand on a half slab
2) Save en exit world
3) Reload world
4) You'll fall down through the slab
Be sure to leave at least one air block beneath the slab to really notice you falling down. It was also reported for the PC version in https://bugs.mojang.com/browse/MC-396
That one was assumed fixed because there was no further feedback from the reporting person. This issue however still exists in the current PS4 Minecraft version.