There could be a problem as you describe. But possibly there are alternate explanations.
But, and I don't mean to discount what you have found, in my case I was pretty darn sure my wife's DNA must have somehow found its way into my sample. Very many of my matches had surnames that matched her ancestry while comparatively very few surnames matched my ancestry. I thought there had to be some sort of problem somewhere
Since then I have concluded her French Canadian ancestry makes her related to just about everyone with French Canadian ancestry. Her grandfather's family is mostly from Quebec and her grandmother's ancestry is mostly from Montreal. Both date back to the earliest settlers, whereas my ancestry is much more limited in that regard.
Your situation is probably different and I only offer the above as an example of an alternate explanation.