Help wanted to understand Ancestry.com ThruLines

[Ellenmai]

I have several DNA matches on Ancestry.com such as 621cM, 265cM, 255cM to name but a few, who I know are descendants from my 2nd Great Grandparents. Yet when I click on the ThruLines 3 of those are showing 0 DNA matches & that I am the currently the only DNA tested descendant connected to this ThruLine. How can this be?

[manukarik]

Thrulines uses other people's trees to find links, not DNA. So will only find a link if you share a common ancestor in a tree, I think...

[Galium]

If your matches have (reasonably) accurate trees which are linked to their DNA result, they should show up in Thrulines. 
(It can be a bit frustrating when you can tell from  someone's tree how they are related to you, but  Thrulines and the common ancestor feature don't work because their tree is unlinked)

[Wexflyer]

If your matches have (reasonably) accurate trees which are linked to their DNA result, they should show up in Thrulines. 
(It can be a bit frustrating when you can tell from  someone's tree how they are related to you, but  Thrulines and the common ancestor feature don't work because their tree is unlinked)

There are three necessary conditions for Thrulines to work:

(1) A DNA match
(2) That the DNA match is linked to a family tree
(3) Sufficient details on either your tree and/or your match's tree for Ancestry to deduce a common line of descent.

[Biggles50]

Ancestry altered their algorithm last Sept, so now we can have odd Thruline results.

Do take their predictions with a whole bag of salt and Evaluate each and every person in the predicted pathway.  Only add each one if you find enough certification and documentation to support their inclusion in your family tree.

I find many errors, many incorrect parentage and even missing generations such that the Mother gave birth well into her 60’s.

Other than as mentioned they can work.

[brigidmac]

You also have to have same spelling + dates for the common ancestors to show
If someone has added lots of punctuation or nicknames ..they will look like different people

Suggest using the also known as option & common ancestors tag rather than writing 2nd great grandfather or whatever as a suffix

[Ellenmai]

Thank you all very much for your replies. I do know three of the relatives who also have the same people on their trees such as a 1st Cousin & have messaged them about this & we are all baffled by it. I had hoped to break down the brick wall to find my Great Grandfather's family, but no match at all there either 

[brigidmac]

Have you checked that they ( & you )

1) have trees

2)have put themselves not one of their ancestors as home person

3)& Have linked their trees to their DNA results

[Ellenmai]

Have checked all three as you have suggested Brigidmac & all done