Portrait Mode on iPhone 11 Pro

The portrait mode is unreliable, especially using the Stage Light, Stage Light Mono and High-Key Light Mono.

1 - Despite being on mono, it most frequently yields a color image

2 - Stage lighting often does not give that effect, reverting back to the standard color Natural light mode, without the spotlight effect.

I've been sure to be the proper distance away and tried both 1x and 2x focal length.

I've shut the phone off and rebooted.

My operating system is up-to-date (13.5.1)

Is there a known problem?

What can be done to remedy this situation?