Pretty much every mod-added slab when placed vertically will have the "missing texture", either all the time or depending on what half of the block that vertical slab was placed. I do have Indium and Micalibria of course.
While some mod-added blocks do work properly, I discovered so far that a lot of slabs from the mod Nookbuild - for example misbehaves in this way. More specifically, I have experimented with colored brick slabs from Nookbuild and all of them behave this way.
Pretty much every mod-added slab when placed vertically will have the "missing texture", either all the time or depending on what half of the block that vertical slab was placed. I do have Indium and Micalibria of course. While some mod-added blocks do work properly, I discovered so far that a lot of slabs from the mod Nookbuild - for example misbehaves in this way. More specifically, I have experimented with colored brick slabs from Nookbuild and all of them behave this way.