Note that you should leave no space inside angle brackets.
You got this error becasue if i remember it right, new version demand that if you use a function that exposed to blueprint, enum have to be exposed to blueprint as well.
All of a sudden UE4 is saying that AEnemy is undefined. So because of that I included Enemy.h at the top. I figured there was some sort of loop going on, since my Structs.h was including Enemy.h, and my Enemy.h was now including my Structs.h
I moved the whole struct that needed to include Enemy.h into another file, which broke the loop, and made everything work!
Although there was a different solution, thanks for the answer. I’ll mark it as correct as it may be a valid answer for someone else with a similar problem.