Probably the full disclosure of account data and behavior has to be shared to find any pattern. Folks who just rent, don't watch and download? Folks with cheapest Amazon account and no Prime Video no ads account? Folks using anonymous IP/VPN (rotating IPs/VPNs?). Normal watch patterns, or just nonstop downloads? Multiple trial periods never continued? Not connected to Movies Anywhere for digital purchase (e.g. Blu-ray) playback? Never use Amazon digital credits to buy digital media? Multiple Amazon accounts started/abandoned?
I downloaded 400 files from Amazon last 7 days. Not flagged. But I don't do any of the things I note above.
In any case - I'm "out" on this topic, personally, as my use patterns do not appear to be trigger for "bad behavior" in the eyes of the Amazon bots. Cheers :) Good luck! 
simchris
Whether it's Prime without ads or with ads, it's not related, and neither are the purchase, rental, refund, and VPN. Get an account without downloading anything on it and use a VPN and rental, purchase, refund, you'll never have a deactivated account.
I use my regular account more than I do for my purchases on Amazon. And this account still serves me with VPN and free Prime Video every month.
I keep another account for download only and email warning amazon concerns section 4.k. 
https://www.primevideo.com/help?nodeId=202095490k. General Restrictions. You may not (i) transfer, copy or display the Digital Content, except as permitted in this Agreement; (ii) sell, rent, lease, distribute, or broadcast any right to the Digital Content; (iii) remove any proprietary notices or labels on the Digital Content; (iv) attempt to disable, bypass, modify, defeat, or otherwise circumvent any digital rights management or other content protection system used as part of the Service; or (v) use the Service or Digital Content for any commercial or illegal purpose.