Well, it SHOULD be exporting whatever you see in the preview for the arch. Basically, we take each node of the arch (or channel for v4 export), create an array of colors, one for each frame in the sequence, then use that array to export the data. Thus, if you have effects on the group or the arch, it should be completely irrelevant when you export a single arch as long as everything is rendered properly. If it's not, then something is wrong someplace.
That said, wait until the 2018.4 as we did a bunch of fixes in the lcb export and in the color[] -> effects so it might already be fixed.