I've just observed some puzzling differences after a TreeShare download - all having to do with Marriage or Marriage Bann events. In one case, an Ancestry Source that must have been linked to the Marriage event in the Ancestry Tree at the time of the download has become disconnected on the AMT. It is linked to the Marriage event in RM and TreeShare Compare shows no such source on the Ancestry side. Browsing Ancestry shows it still in the Sources but connected to nothing while its Marriage event is now connected to what is called an Other Sources > Unsourced Citation with no data.
Another Marriage Bann event that matches on both sides shows the 1 source each has as different and a new source for the other. But they are the same source.
There are other weird ones.