How is the CRON running? Is it possible it is using the IP address instead of the domain to access the site? I suppose a CRON could use localhost as well, but you should be able to control that and have it use a recognized domain.
Maybe add the IP address to the list of domains? The problem is that somehow someone or something is accessing the site using a different domain than the ones you have listed. You just need to figure out how that would happen and account for it.
Another temporary solution would be to set the default connection to the live settings so that they will work when accessed from a different domain.