I get that this is 6 years old - but did you happen to find the answer out?

Apple developer enterprise program is not used to distribute apps via the normal App Store. Its more for internal app distribution within your own company.

I'll close the loop on this - it just took time. The magic threshold of 5 unique devices must be more complicated than just that. Eventually, the reports did come through. So if you use campaigns to generate a link - just wait more time.