When using the combination of a single Smart Object, Artboards and Export As, Photoshop alters the displayed position of elements. I had a single Smart Object -- a column of four icons copied from InDesign. I wanted to break that column into four separate icons. I created four identically sized artboards and copied/pasted the Smart Object onto each, carefully positioning each icon so they were vertically centered in the artboard. When I did Export As, Photoshop appeared to be removing my careful vertical positioning; all the icons became top aligned in the Export As preview. I had to rasterize the Smart Object, select the icon with the marquee tool, cut it, then paste it into the artboard to lock down the desired positioning.