Noise adjustments applied do not show on Ipad when image is reloaded . You have to 'tap' on the image for it to update each time you move off image to another and come back to it. Exports with NR applied, but frustrating when scrolling through images.
I just tested on my iPad Pro (2016) and I don't see what you are seeing. There is about a half-second delay in the Noise Reduction rendering but it does appear on its own without having to tap on the screen.
If you swipe to a new image and don't tap, does it every actually render the noise reduction or does it sit there for minutes without rendering?