I also see strange anomalies in the sync log, and I know there has been at least one discussion about it on this board, since the sync change log was introduced.
If, for example, I have added a media item to 1 person, it will often show up, in the log only, as related to dozens of other people. I have verified in my tree, both online and in FTM, that the media item is only attached to the 1 correct person.
So, IMHO, the new sync change log is pretty useless. I do keep copies, but between this persistent error and the truncation of source detail, it cannot be relied on.