Issue with mutual matches

[Liviani]

Hello all.

Wondering if anyone can help me with an issue that seems to keep happening on various DNA testing sites.

I have done tests with Ancestry, 23andMe and Living DNA. I have uploaded my DNA data to My Heritage, GEDmatch and FTDNA. My mother has tested with My Heritage recently.

I have a match who I will name as GC. We talk regularly via email and have done since last summer. At present we have not identified where we match. I have the feeling there is a NPE that is confusing matters. I initially did DNA to find my unknown 2x great grandfather. Unfortunately this hasn't succeeded at this stage.

We have quite a lot of mutual matches, many with Irish ancestry so we feel it comes from there.

There is a problem, and I don't know if this is a common problem.

I match GC with ~40cM. My mum matches GC at ~10cM

My maternal first cousin has tested with 23andMe and GC is showing as a mutual match with him. My cousin matches GC with 0.13% shared DNA which translates to approx 9.62cM. However my first cousin is not showing up as a match for GC at all.

There are other cases of this happening elsewhere, and with matches who have a decent match size with us. One matches me on GEDmatch at ~22 cM. He is a mutual and a triangulation with GC and myself. GC confirms this man is also on Ancestry and shows as a match for him there. However, on Ancestry for me this other person is nowhere to be seen. There are others like this across many sites.

I match GC on Chr 2 and 20. My mother matches GC on Chr 2 only. She does not match anyone of GC and I's mutual Chr 20 matches. GC suggests that it's possible Chr 2 is a mutual maternal match and Chr 20 is paternal. Which is possible, the majority of my ancestry on both sides are from quite condensed areas.

It's all very puzzling and feel it's hampering us solving where GC and I match.