So I found out the answer was simple. Turns out if you ever installed Unreal and you later have your environment Temp & TMP paths changed at all(probably to free up space on your C:), then the launcher will fail. You can test this by making another user, and if the launcher works on that account and not yours then you can be sure it the environment variable. Just go to your system settings and set them both back to:
%USERPROFILE%\AppData\Local\Temp
After a restart that should fix the problem.