But, it still seemed to happen - on all browsers, Chrome, Firefox, Brave and Safari. So it must be my MAC - where next? Well, watching Amazon Sport using a Private browser Window seemed to be the answer. What is loading and causing Safari to loose video quality? It's not the few extensions (switched off-even uninstalled) - it's not WiFi (used Ethernet connection the router) but, Private browsing fixes the problem - why? Don't know.