Thanks for that info. For issues with a particular movie from the iTunes Store, you can use the Report a problem-link in the invoice e-mail or use the reportaproblem.apple.com website. For issues with a particular movie from a third party distributor (Netflix, Amazon, Mubi, etc.), you will have to contact them directly. Their support website may have feedback links for that.
If the issue is with just one movie, then the problem may very well be on the source side of the network, and all you can do is ask for the distributor to fix it.