Mod Missing many elements when exported and then tested. (1.15.2) (2020.5)

Hello o/
I have been working on a 1.15.2 mod for a while now called Arcania. Recently I have been unable to test the exporting and playing of the mod as many items have been missing from the exported version. Everything missing physically is still in the jar file as code and textures, except the fact that it doesn't appear in game.

I am using Mcreator 2020.5 and the mod is for 1.15.2 forge.
I will attach the file.

Thanks :)