you read that right
crash-client.txt

Hi there! Apologies for the extremely delayed response to this issue, had a really hectic year at university so haven't got round to checking the issues with the mod. Can you explain to me how you produced this? Thanks

Hi! No problems, school and work are important things.
I saw that air slab in my mod pack and i tested this mod only with jei and latest forge (2860).
You can also get it without jei, with commands.
Very interesting block ngl.

I would either keep it and add some properties (because it crashes when player tries to break it or walks into it) or default slab`s properies to stone slab.

or walks into it

Crash only occurs when player interacts with block hit box, sometimes game kicks for invalid move player packet receive, or crashes with code (-805306369) without crash report.

Atleast this is what I have observed.