"Flat" isn't really a preset. It's just the default when you open an image. The only value that changes with "Flat" is the tint, usually by such a small amount (+/- ~10) that it's barely noticeable.
Try using a much more obvious preset and export that.
I've just done a test with the "Camera > High Contrast" preset and the image exports correctly.
There is a big difference between the presets that you can choose while shooting in camera mode and the presets in editing mode.
I stopped using the in camera presets and edited each and every file afterwards. A bit annoying ...
for me the "flat" style makes a huge difference compared to the unfiltered image.
Without filter: Dropbox - Foto 26.02.17, 18 35 49.png
flat style: Dropbox - Foto 26.02.17, 18 35 53.png
So maybe to clarify: i am using the Lightroom mobile app on an iPhone 7+ and shooting in DNG.
While shooting im using the (German: Flach / English: Flat) quickpreset.
This results in an image while shooting that I really like. (1)
in the gallery the pictures are shown in this style.(1) But when i export them without any edit the pictures are plain - like the raw file. (2)
compared this to the "flat" preset in the editing mode (3) it doesn't look a bit like the one I shot (1).
Maybe the difference lies in the way Lightroom mobile works. I guess there is some sort of preview file that is created on the fly. But when you are loading the raw file the preset etc is not matched correctly because of the different bit-depth.
Yeah, that's quite a difference. What happens when you view the photos in Lightroom Desktop?