Sometimes, infrequently, my test and control do not add up correctly. For example, let's say my test group is 10K unique visitors and my control is also 10K. I would expect my activity total unique visitors to be 20K, but sometimes I see something lower than expected (i.e. 19,998). Can you explain why this occurs?
I've seen cases where Analytics for Target was enabled and there was a redirect on one of the experiences and the totals for ExpA + ExpB were above 100% in those cases the reason was because every once in a while credit was given to both the original and final destination due to the speed at which calls fired (race condition) however this appears to be a little different perhaps you can share a redacted screen-shot of a report showing this. Either way if you want to open a ticket with support we can help you look into the details.
If this satisfies your query please like, mark as helpful and mark as answer. Otherwise lets keep the conversation going. Hope you have a wonderful day.