I've forwarded the extra data to the address you provided.
The list was created after we'd installed Sugarchimp. It was populated into Mailchimp in one hit via a target list from Sugar. The updates that should have happened were all after that initial setup.
I've done a spot check and the ones that aren't synchronising back are still present on our target list so I presume the link is still intact.
Also, on the problem dates we see a few that have synchronised back, which is difficult to explain.
The data I sent just shows email address, date/time and if it synchronised or not. So it shows the time distribution of the problem but not much else... please let me know what other data you need to diagnose.