The following slabs lose their custom name after leaving and rejoining the world:

• Cobblestone Slab
• Stone Brick Slab
• Brick Slab
• Nether Brick Slab
• Quartz Slab
• Sandstone Slab
• Smooth Stone Slab

Steps to Reproduce:

1. Rename any of the slabs listed above in an anvil
2. Leave and rejoin the world
3. Check the slab's name

Observed Results:
The name wasn't saved.

Expected Results:
The name should be saved.

https://streamable.com/y6bo9a