QWindow with Metal backend freezes when reparented across screens

On a Mac that has two or more physical screens:

• Create a QWindow using the Metal rendering backend.
• Render a new frame to the QWindow every time it receives a QEvent::UpdateRequest
• Host the QWindow inside a top-level QWidget using QWidget::createWindowContainer()
• Reparent the container Widget into another toplevel QWidget

If both toplevel QWidgets are on the same physical screen, rendering continues as expected.

If the other toplevel QWidget is on a different screen, UpdateRequest events cease being delivered and the animation freezes.

The issue occurs with both QRhi and 'native' Metal.

See qtbase/tests/manual/rhi/multiwindow for a base example.