Hi,
The selection of page pointers has been changed in 7.1 so it is context based instead of channel based. If you upgrade it from 7.0 it is possible that the channel ids have been removed from the page pointers. Order carrier has also channel id. Change the return row as follows.
return _urlService.GetUrl(_pageService.Get(pointerPage.EntitySystemId), new PageUrlArgs(pointerPage.ChannelSystemId != Guid.Empty ? pointerPage.ChannelSystemId : orderCarrier.ChannelID));