Why had Gedmatch and Genesis given extremely different "X" comparison results?

Question

When I uploaded the same DNA kits originally from 23andMe, to Gedmatch and then to Genesis Gedmatch,  I did an "X" comparison with a close relative. (both females).

The Gedmatch agreed with 23andMe results, sharing 91 on the 23rd chromosome.

But Genesis with the same DNA kits  comparing "X" said no DNA shared.

That is a huge difference.

I am using this DNA to prove my biological grandmother, so it is very important.

Why would this be, and which is correct?

Answer 1

http://blog.kittycooper.com/2017/12/genesis-from-gedmatch-the-new-chip/

It is known that cousin matching is affected as the 2 chips only share a small amount of overlap for comparison it seems.  

I guess where they overlap there is value but if they don't it it likely because they don't have the data to do the match.  So an absence of a match does not mean anything as it is likely from lack of data.  

I am sure someone more knowledgeable than me will give you a better answer.