On Ancestry I have a match at the 3rd cousin level and we have common matches with both my mother and fathers side. New to this and that is confusing to me. Sorry if I am missing something obvious!
This may simply mean that you and your match are simultaneously related in two different ways. Just as one example of this, you two could be related in these two ways:
- As third cousins through your father's side - one set of your paternal great-great-grandparents are also a (paternal or maternal) set of great-great-grandparents of your match, and
- As fourth cousins through your mother's side - one set of your maternal great-great-great-grandparents are also a (paternal or maternal) set of great-great-great-grandparents of your match.
This is just one of many similar variations of possible relationships that you and your match could share. Figuring out just which possibility is the right one would require that you and your match have or are able to obtain traditional genealogical information about your respective ancestors back to the generations in which you are related.
Agree with the first two answers entirely but it is also worth remembering that DNA segment transmission is random. It also does not say exactly so much of this chromosome goes here and so much there. It could be a large piece of one chromosome and that stays intact giving a false DNA reading? I have a number of same surname marriages as evidence of natural returns of DNA? I am not sure this would give third cousin readings but it would not be straight reading of the result. Just some thoughts?