Blaine T. Bettinger, the Genetic Genealogist, has created a YouTube video (12 minutes long) titled: Why Don’t I Share the Same Amount of DNA With Cousin X at Every Company? – https://www.youtube.com/watch?v=Veb6vn_BFRY He created the video since the question comes up on a regular basis. Here’s the blurb from YouTube:
If you have a cousin that has tested at more than one company (23andMe, AncestryDNA, Family Tree DNA, MyHeritage, etc.), you may have noticed that you share different amounts of DNA at different companies. For example, you may share 67 cM at Family Tree DNA and only 45 cM at AncestryDNA. Shouldn’t you share the same amount at every company? If not, why not? Let’s look at a real-life example!
You can learn more about Blaine at https://thegeneticgenealogist.com/. You can also see him on Facebook in this group: https://www.facebook.com/groups/geneticgenealogytipsandtechniques/.