After a failed attempt with Netflix chat support I finally figured out the problem myself. My issue was close to this, but Netflix kept rate selecting 4K HDR down to a broken 240p stream (with about sixteen screwed up blocks on screen). The NetFlix connection tests all passed. The link said it was fine (50Mb/s). I event rebooted my BT home hub 6.
So the solution was both annoyingly simple and unpublished.
For Sony Android TVs you basically need to nuke Netflix in the Settings. Go to Settings, into the Apps and track right until you find NetFlix. Uninstall all the updates and clear all the settings and caches.
When you start Netflix again you'll need to log in, but this instantly fixed my long standing 4K HDR problem. I got wise to it as when I clicked on the NetFlix Storage option in Settings it said I was out of storage (it had used 96KB where there was GBs free).
Lesson learnt. And yet again, never contact tech support. They're useless.
My take on this problem is that subsequent updates pushed out by NetFlix for the app result in old data getting corrupted and then this adversely effects how it works.
