When Google Scholar comes across papers written by people with similar names, it assumes duplication and includes only one name, causing a missed or omitted citation for the other paper/author.
#Reference manager 12 not working with google scholar registration
Google Scholar: Apart from restricted or blocked access, Google Scholar does not check articles on sites with any form of conditional access, such as a registration (log-in) or a subscription. So too if the journal site now has a protocol excluding search robots. Also, if the journal was open access earlier but is paywalled now, Google Scholar will not be able to access it any longer. If the journal is not open access, you may not be able to check this without making a payment. They may even have removed your reference from your paper. For instance, they may have changed the way they write your name or the title of your paper. The author(s) of that article may have made some changes to the formatting or the references/ citations section of the article. Other article or journal: There may have been some changes to the other article or to the journal (site) in these three years. There are several possibilities why this could have happened – on the side of the other article or journal, on the side of Google Scholar, or on your side.