One of my papers on Google scholar used to have 5 citations. It later went down to 4 and is now on 3. My other papers are monotonically increasing. But I've had this one paper that seems to have lost 2. What might be some reasons for this? Assuming Google Scholar did some checks and found some of them didn't meet certain criteria, just curious what those might be.
This happened a couple of times to me, mostly because of duplicates: GS had the same paper indexed twice, which lead to duplicate citations for some of my papers. The duplicate entry was removed at some point, and with it the duplicate citations.
In another case, a paper published informally online was removed from the website, and then also from GS, which lead to citations to my papers being removed as well.
Both cases could be formulated as a "criterion" that Google validates in some internal "check" (no duplicates, online-only resources have to be permanent).