I am by far no expert, but I had the same issue and was unable to find any answers. As a last resort, before asking my geek friends 
I thought I would try something that fixed an issue for me in another game, it worked … maybe it will help you too.
(I am running windows 10 on a PC)
- Click the start button and do a search for windows defender security center
- Go to virus & threat protection and scroll down to click on ransomware protection
- I had “controlled folder access” active … if you do as well, you can either turn that off while you install the epic launcher or you have to allow that app through.
I opted to turn it off … then I ran the install .exe for the epic launcher again and it installed just fine.
Then I went back in and turned controlled folder access back on (cause I figured it was on for a reason
Hope this helps you as well or that someone smarter than me, replies to your post,