When placing 2 different double vertical slabs near other vertical slabs some of the textures don't render properly. This only happens when two different slabs are placed together in one block and only affects textures of the slab that has been placed first. Horizontal slabs don't have/cause this issue. I do use optifine, however disabling it or changing any options doesn't solve the problem.

Hi, thanks for the report! I've tried to reproduce this myself and can't seem to do so. Have you tried reloading the textures?

Hi there! Apologies for the extremely delayed response. This is now fixed in the latest version :)