We use Citybridge as a wellington-auckland transit provider and at one point we had an issue with the OSPF that underpins our BGP and LSPs.�� The issue wasn't immediately apparent when we commissioned the service but appeared abruptly a few weeks later.
The incident report stated that they had to increase the Multicast limit on the transit.�� Not particularly clear on what limits were in place or why they suddenly became an issue but its pretty clear that there is some multicast manipulation in place.
I would suggest taking this back to Citylink again, i'm guessing that getting a man in the middle to test each leg of the transit is not going to happen?