So it appears somehow Sonic thinks your mac address 00:0C:29:BE:FA:B5 belongs in some other port than what you are connected to and will send all incoming packets there unless you send a probe to move the address back to you. I don't think someone else is using exactly the same address. If they were, there should be many more losses because every time they sent a packet the address would move to their port. I would guess that the address is somehow configured to a port that's not yours, or possibly the dslam mac table has hit an error. Now that you no longer use 00:0C:29:BE:FA:B5, Sonic support should be able to look at whether the address is stuck somewhere.
Dear Sonic Support,
If you are following this thread at all, can you check to see if that MAC address is in the DSLAM cache presently? If so, it's not me! I'd love to know one way or the other.
Anyway, my pingout script was doing a ping count of 2 and logging the responses and my logs showed that there were many cases in which only one response was received. So the symptom does appear to suggest that someone else was/is using that same MAC address and we have been ping-ponging the MAC port mapping.