Acording to the duplicates from this issue, it looks like you can't move the screen in a slow motion because of a potential increased Deadzone on joysticks, giving a bad experience at playing parkour maps (MCPE-163044) or making it harder, for example, to make adjustments with bows to make the arrow hit your target properly. Basically, you cannot progressive look with a joystick anymore (gathered information from MCPE-162990.)

Potential steps to reproduce

1. Set your sensibility to 100, to better experience the issue
2. Try to very slowly turn around the screen
3. Notice how it only turns with a fast movement

Expected

The screen turns around very slowly.

Actual

You can't move the screen slowly. It only moves with fast movement.

This is why the speculation is a increased deadzone of the joystick. A bigger deadzone means a smaller area of the joystick where you are able to move the screen slowly.

Note: This ONLY started to happen after the new performance update. This also affects the preview version of the game, possibly since its initial release.