Citations are identified automatically by algorithms, not manually. Therefore the ResearchGate (RG) team cannot help you to find more citations. There are several reasons why the lists of citations in ResearchGate are rather often incomplete, e.g. missing full texts of the citing publications in RG. Also RG's algorithm is far from being perfect. See also these discussions (only a selection - the question of missing citations is one of the most frequently one asked here):

https://www.researchgate.net/post/Why_citation_score_for_author_publications_looks_different_on_Scopus_research_gate_google_scholar

https://www.researchgate.net/post/Why_are_some_citations_not_visible_on_ResearchGate_and_Google_Scholar

https://www.researchgate.net/post/RG-citations-how-are-they-calculated/1

https://www.researchgate.net/post/missing_citation_number/1

https://www.researchgate.net/post/Why_are_some_of_my_citations_not_shown2/1

https://www.researchgate.net/post/Why_the_citation_is_not_shown/1

https://www.researchgate.net/post/How_can_we_add_citation_on_research_gate/1

https://www.researchgate.net/post/How_add_references/1

https://www.researchgate.net/post/Citations_from_RG/1

https://www.researchgate.net/post/citations_in_RG/1

https://www.researchgate.net/post/How_do_you_fix_missing_citations/1

https://www.researchgate.net/post/How_to_add_missing_citation/1

https://www.researchgate.net/post/What_if_I_have_citations_in_the_research_gate_indexed_papers_that_research_gate_does_not_show_them/1

https://www.researchgate.net/post/Question_about_article_submitted_and_references_does_not_appear/1

https://www.researchgate.net/post/RG_system_to_detected_Citations/1

Good question, thanks..

Really it completely depends on the data base for each academic platforms.

Wish you all the best..

Regards, Emad