Where are you exporting them?
Did you try to save them to the CC libraries and then check?
No, I did "Save To Gallery". Do you mean that it is not possible to save to gallery with the original resolution?
I tried "Save to CC Library" but I do not find the file after export.
There could be a possibility that the high res capability is not getting sustained to your device gallery.
Saving the work to CC libraries can be a workaround just to check if the high res work is getting saved or not.