In ResearchGate, all citations are identified by automated algorithms, and these are far from being perfect. There are also other reasons for missing citations, e.g. that the citing or the cited publications are not in RG's database and thus cannot be identified. See also https://www.researchgate.net/post/Why_citation_score_for_author_publications_looks_different_on_Scopus_research_gate_google_scholar and many more discussions on the question of missing citations I listed therein.

Dear Klaus Hauer In addition to what is already indicated by Wolfgang R. Dick I see that for example one of your references has the title

The Medical Costs of Fatal Falls and Fall Injuries among Older Adults

While the correct title is (in the final publication)

Medical Costs of Fatal and Nonfatal Falls in Older Adults

This might be one of the reasons that the RG algorithm cannot recognise this one.

It might help to upload the pdf file (as far as I can see it is an open access paper so it is allowed). This might lead to more recognised references and I would like to add that after some time RG recognise more references so the problem might resolve itself (somewhat).

Best regards.

dear Rob, dear Wolfganf, thanks very muich for the prompt response. i was aware of the fact that the search is perfromed by algorithms and that there might be a loss of citations. The poptentail causes mentioned do not qualify for this issue, we check for the wrong citation (which max not be modified now). of course other reason may be relevant. It was only that in a most recent review of our lab 34 out of 176 refs were lost which is substantial. it is a pity for the authors referenced not getting the attention (and reward being listed) for their work.