Could be ports:
http://www.toolzz.com/?p=749
could be fqdn on your sup, or custom categories/products from SCUP
https://social.technet.microsoft.com/Forums/systemcenter/en-US/27e6d79c-103b-4f77-bdf0-a564f5f4d4ba/sms-server-6703-sms-wsus-synchronization-failed?forum=configmgrsum
Or... if it's working fine anyway...just ignore it...