StageVideo Fails from AIR20 on Flexmobile / IOS

Our IOS Flexmobile project has played StageVideo beautifully for many year and Air updates. That's until we created a new version with AIR 20, ( and 21, 22Beta )

No video code changes were made since the AIR 19 SDK version which plays stage video perfectly.

Here's the fault:

StageVideoAvailabilityEvent  returns "available".

So we try to attachNetStream but it fails to render.

However the StageVideoEvent.RENDER_STATE  returns StageVideo Render Status (software/hardware):unavailable

We use vimeo pro for the video and are compiling on Windows with FB 4.7.

The IPAD 2  is running IOS 9.2

We're using bog standard StageVideo code :

protected function onStageVideoAvailable(event:StageVideoAvailabilityEvent):void

  {

  if (event.availability == "available")

  {

  stage.removeEventListener(StageVideoAvailabilityEvent.STAGE_VIDEO_AVAILABILITY, onStageVideoAvailable);

  sv = stage.stageVideos[0];

  sv.attachNetStream(ns);

  sv.addEventListener(StageVideoEvent.RENDER_STATE, onRenderState);

  sv.viewPort = new Rectangle(point.x, point.y, kvidFrame.videoWidth, kvidFrame.videoHeight);

  stageVideoSetup = true;

  if(ns){

        ns.play(getSourceDef(videoToPlayVid));

        this.setStyle('backgroundAlpha', '0.0')

  }

. . . .