Strange behaviour after modifying exposure duration and going back to AVCaptureExposureModeContinuousAutoExposure

When I set a custom exposure duration, like 1/8, and then switch back to continuous auto exposure, the exposure duration in areas that were previously 1/17 changes to something like 1/5 or 1/10. As a result, the screen becomes laggy and overexposed. I'm not sure why this is happening.

Strange behaviour after modifying exposure duration and going back to AVCaptureExposureModeContinuousAutoExposure
 
 
Q