21CN Line Rate Data

I was looking at the Line Rate Data available in the Zen customer portal, mainly to try and correlate an issue I'm having with ever-decreasing sync rates.

I noticed that I have data available (i.e. a new "Sync Date") every 2 days. Is this actually supposed to represent a sync event, or is it simply BT feeding information over to the ISP at a regular interval?

My router holds sync for longer than 2 days!

For background teh problem I'm having is a very good fast line re-syncing out of the blue, and connecting again at >6MBps slower than the line is capable of. I'm getting interleaving forced on, as I think that may be the issue (line changing to FAST, and a burst of errors kicking it off).