I'm running PanOS 9.0 on a PA220 and noticed a couple days ago that Amazon Prime Video wasn't playing on any of my wireless devices. However, it would play on a desktop or laptop through Firefox. After a few troubleshooting steps and Google, it seemed to me the difference was in the actual player itself. I enabled "Allow HTTP partial response" in the content-ID and everything started working. I'm not sure if this is a bug or not, but I think it's probably working as designed. This option prevents a client from resuming download of a malware file if the firewall stops the download, so it is unfortunate that it needs to be enabled for this to work.