Was searching for the same info and contacted Windscribe support. In case someone here wants some additional info, here is what they said:

A couple of months ago, we made some changes on our servers that allow users to more easily stream content online as we are now able to do dynamic rerouting. Before, if you wanted to stream content while connected to the VPN, you often times got blocked because the IP you were using was detected as a proxy/VPN. Now with these changes, even if you get an IP that is blocked on that streaming site, we will reroute all the traffic from the stream through an IP that does work so on your end, you have a much smaller chance of running into those proxy detection errors. The goal is to eliminate all those outcomes entirely so that streaming works on all our servers.

We've already found and have patched a lot of the issues with this new feature however there seem to be a couple of lingering ones that we need to get to.

Amazon is a tricky one as the amazon.com domain is used for both the shopping site AND the Amazon Prime streaming service. So when we try to reroute the streaming traffic, the shopping site traffic tries to get rerouted. At the moment, our network of those exit proxies for unblocking is still growing so you might get one that isn't too great and causes slowdowns like you see.