I've setup a windmill, but the block moving through the mechanical bearing are invisible. It's on a server and my friend can see it perfectly, it's working fine, adding rotating force to the system and I can even see the rotating part of the mechanical bearing moving, but not the pale itself

Are you using Optifine and Shaders?

Solved : Updating Forge solve it, I had a forge prior to 28.2, my bad.