Reddit and BlueGartr have narrowed down that just the NA client is not getting the Play button. JP and EU clients work to log in. All clients use the same files except for the region marked in the FFXI and layOnline applications, but it is hard to install both together. If you can just install PlayOnline Viewer for EU and set up the registry entries for FFXI of that region, you may have to only do a file check, but no redownload.