[SOLVED] Rotated faces are black on 3D model block

Hi. I'm having an issue with a custom 3D model I have made for a block.

I'm using MrCrayfishs model maker. I make the model in the program and it looks like this:

I import the model in Mcreator and run the game. But then ingame the model has weird black edges on the rotated parts:

Any help would be much appreciated. Thanks!