Photoshop "Export as" quality problem

@Stephen Marshgood tip, thank you.

I am tried using legacy export in preferences, I also tried uncheck "multithreaded compositing" but solves nothing. 😞

@D Fosse 

Good points, I'll double check my export prefs. The devs should be able to replicate the case from the sample.

@Payne66 - As flattening is destructive, I personally favour merging visible layers to a new layer, but as long as you're careful you should be OK.

I've now tested Export As with layered and flat files.

They are absolutely identical. Difference blend mode is absolutely black down to the last pixel.

So if this is a bug, it's not universal. The question then is to determine what conditions it happens under, so that it can be reproduced. Are you using "legacy export"? I'm not, I'm using the current one, v 5.8.34 - Photoshop 25.3.1, Windows 10 pro.

EDIT - there is a preference checkbox for "multithreaded compositing". Not sure what it means, but try to uncheck it. I seem to remember there once was a "GPU compositing" checkbox, but that went away.

@Stephen Marshand @D Fosse, thank you both for your help.
If I flatten the image Export as looks normal to me. This is solution I need for now. Thank you again.

From time to time we do see reports of buggy behavior with layer compositing in general, here in the forum.

This can take many forms, Export naturally being one of them as it needs to merge as part of the process. I don't have an opinion about what's causing it, just something we see here from time to time.

@Payne66 

Thanks for posting the image as requested.

This needs further testing... My first result using Export As with Bicubic Smoother resampling to 1920px wide actually appears to use Nearest Neighbour resampling (Ps 25.3.1 on Intel Mac, Monterey)! I don't believe that user error was the case, but it's also hard to believe that Export As would be ignoring the selected resampling method and using the worst method instead for photographic reduction :]

Thank you very much for testing @D Fosse.
I dont understant why this is happening to me in Photoshop.

Can I ask you for help again?

Here is the mockup I using: WeTransfer - Magazine mockup 
Can you download it and test it like you did with dragon fly?
Try downscale it to 1920x1080 in export setting and save it with Save for web (Legacy) and Export as.

Then post it here please.