Recently I've been taking special notice of X-DNA matches, and I've come across several DNA matches where the X-DNA cM value is very high (but the atDNA cM value is very low). I have first cousins with smaller X-DNA cM values, but their atDNA cM value always are within the expected amount for a first cousin.
An example from GEDmatch is:
I'm wondering if a match with such a large X-DNA cM value is always valid (or can this be a false-positive result)?
If this is a valid match, it posses a problem because the two donors/matches don't share a "common ancestor" (which should be at most a few generations away).