Most probably, you just removed these papers from your profile, but they are still in ResearchGate. You just have to claim your authorship again. 1. Look into https://www.researchgate.net/profile/Bettina-Siebers/unconfirmed (visible only to you). 2. Search for the titles of missing papers at https://www.researchgate.net/search.Search.html?query=&type=publication.
See also https://help.researchgate.net/hc/en-us/articles/14293005132305-How-to-add-research.