In ResearchGate (but also on other platforms), the identification of citations is often not complete. There is an automated algorithm for identifying citations, but this is far from being perfect. See also these related discussions about missing citations:
This section gives only the number of mentions, but not of citations. These are different things, although some of the mentions may be also citations. I also noted that Academia.edu seems to identify me with other persons of similar names. They regularly send me messages about mentions to announce their premium version. But several of the fields of papers allegedly mentioning me are far away from my own fields, so I am convinced these are misidentifications.