Photoshop Question about Adjustment Layers not Saving Properly

I hope my reply helps because I may be discussing an issue that is not relevant to your question, but I think it will help some people with a confusing problem that I needed to solve. I apply many layers (smart layers, filters and adjustment layers) to my work and I found a long time ago that when an image is flattened, some effects will no longer be what I see on the screen. If I have changed the opacity of layers, especially when using blending options, I found that, prior to printing an image with many layers, it's a good idea to make a "snapshot" of the image first. On a PC, what you do is select the very top layer and then hold down Shift + Control+ Alt while pressing the "e" key. This "snapshot" is the identical image, with all of the correct layer properties that you see on the screen. So, if you want to save the image as a jpeg or a png, you can simply duplicate the entire image after you create the snapshot, and then in the duplicate you can delete all of the layers below the snapshot, making the file much smaller.  You should, of course, also save the original image keeping all the layers for future revisions as a psd or a tiff, etc. 

I had this same problem yesterday ( I could not print my image as I saw it on the screen) and this is how I found your post. I had an idea of what may have caused Photoshop to not print the Threshold layers, so I tried an experiment and it worked. I was applying the Threshold layers to a smart object layer. Since I also had the original layer saved, I copied all of my Threshold layers to it and deleted all of the smart objects and smart layers. By doing this I was able to print only B&W without gray. The smart layers that I had applied (which were Ink Outlines and Poster Edges) did not need to be reproduced on the original layer because they had no effect once I applied Theshold layers. If you still would like to fix that one image that was giving you a problem, try this method, but be sure to make a duplicate image and only apply thr changes to that image. Just because it worked for me doesn't mean that it will work for you.

Would you be able to share a screenshot of your entire screen? That way we can see your panels and it might give us better understanding to what's happening.

You need to view at 100% for an accurate adjustment preview. At any other zoom ratio the preview is not reliable.

For performance reasons, adjustment previews are calculated based on on-screen zoom ratio. Zoomed out, that's a down-scaled, downsampled version.

This happens when you have sharp pixel-level transitions, such as very noisy images, very fine detail, line art, halftone screens etc.The resampling (scaling) softens and blurs the image, resulting in intermediate levels not really there in the original. So when you commit and the calculation is performed on the full data, the effect seems to disappear. But in reality it was never there to begin with!

In a "normal" photograph this isn't an issue. It just happens in the circumstances mentioned above, and when you know that's the case, make it a habit to always check at 100% view.

You have to watch out for what's underneath transparency.

This is a gradient that includes 50% transparency at the top of the gradient, but there's nothing underneath it because I've hidden the background layer...

...or there might be no Background layer

JPEG doesn't allow transparency, so when the layer gets flattened during the export it changes color because it gets merged with the canvas whether there's a background layer or not:

I need to show the filled background layer to show the effect of flattening in the JPEG in the layered version

The JPEG

Could you please post a screenshot of the layered file taken at View > 100% with the pertinent Panels (Layers, Channels, Options Bar, …) visible and the resulting jpg?