The references may not have been extracted correctly: ResearchGate uses automated tools to extract references from uploaded articles. Sometimes, these tools may not be able to extract all references correctly, especially if the formatting of the references is not consistent or the text is not clear. In this case, you may need to manually add or correct the references on ResearchGate.
The article may not have been fully processed: It may take some time for ResearchGate to fully process and display all the information in your uploaded article, including the references. If you have just uploaded your article, it may take some time for the references to appear.
If you have checked these possibilities and are still experiencing issues, you can contact ResearchGate's support team for assistance.
See the method by Andrejs Krauklis to improve the identification of references by ResearchGate's algorithm: https://www.researchgate.net/post/Method_for_Improving_Recognition_of_Citations_References_on_ResearchGate . My experience is that sometimes this method works, sometimes not.