Download the sample file(image) below:

1.1 What the image looks alike in 100% normal view mode (with dark background) 1.1 Zoom to 801% or 1132%, you can see bright lines that do not exist, this is the error of resampling method
2. Bad quality in edit mode (crop, etc.)
2.1 Watch my reproduction steps in the animation image below

Which is
2.1.1 Open any image then zoom out ( let MP using downscale method)
2.1.2 Click crop image
2.1.3 You may noticed that exiting crop mode won't fix that, neither do changing image. Because it was cached, you have to refresh it. One method I've found is click option button then cancel it.
2.2 The different between downscale method of view mode and edit mode (sorry for the typo)
BTW, MP should let users be able to customize the upscaling/downscaling method, in both view mode and edit mode.