It turns out it wasn't a GeoServer or network/firewall setting, but that the source data was not in an agreeable projection though I had set GS to reproject to 3857.
I had been trying to edit a multipolygon layer, and even though I was drawing inside the bounding box, the reprojection was moving it someplace else well outside the bbox and I can only assume this was causing the rejection. I discovered this when I tried editing a point layer in the same projection, but apparently it isn't as picky about the bbox as it was accepting it, but well outside the bbox. I only discovered this when as iant suggested looking at the log file that I saw the attributes that I had assigned to a point showing up and used QGIS to confirm that the point had in fact came through, just nowhere near where I had placed it. Once I transformed the projections of the PostGIS tables to 3857 and removed and brought them back into GS, both were editing as expected.
But it is interesting that on network wasn't affected by the projection difference, but outside the network it was (I don't know if this would be considered a bug).
Thank you everyone for your help.