There is not a specific way to cause this bug, it happens randomly.

In some structures, shadows can appear black and opaque. It mostly happens in caves entrances, structures with stairs and slabs, mountains or cliffs with outstanding blocks and it happened to me using redstone lamps as well.

It usually affects the same structures everytime, you can place a block in the shadow to fix it but once you open the world again the shadow returns being opaque.

This bug is really annoying so please try to fix it! We will appreciate it.