I think the xem is correct, the problem on my tracker at least is that different groups are using different episode numbers. Most of the releases on the tracker are using the xem numbers, but there are two groups that are using the tvdb numbers instead, which means that sonarr is downloading the same episode twice each week.
The only solution I’ve found so far is to blacklist the groups using the tvdb numbers using the method here: Is it possible to blacklist an episode without downloading it?