I had the same issue, i was working on ATM screens, we needed them to be exactly, but some screens have 1 px more..
the problem that we sometimes move the artboard by mistake some part of pixels.
for example below position on canvus, when you export the size will be the same.
below example have part of pixels, the resulet when export will be 971px X 545px
to fix this problem is make sure that nothing are locked, go to artboard panel, rearrange the artnoards.
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