Can you show some screen shots? I'm not seeing this happen.
You must view at 100% for a reliable preview of adjustments.The adjustment effect you're seeing in the preview is an artifact, not real.
For performance reasons, adjustment previews are calculated based on the on-screen image. At other zoom ratios than 100%, this is a scaled/resampled and therefore softened version. This introduces mid-tone values where none are in the original.
Halftone screens, or black and white line art, will show this very dramatically. But also very noisy images, like a starry night sky.
It is pretty difficult to know what is happening with your first question. If you can share a screen capture of the image and the levels settings we might be able to help.
For question #2, it's possible that the other program you are using can't read the layers, and non destructive edits of a levels adjustment layer as you are describing. What is the 'other' program you are viewing the file with?
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With Levels "not taking", it's always about not viewing at 100%. Wait and see