Hi @MA1985_CG PLease look at the following post, you'll get hopefully the information needed https://experienceleaguecommunities.adobe.com/t5/adobe-experience-platform-data/profile-merge-issues-since-ecid-is-same-when-multiple-users/m-p/650556?action=reply&id=650452#M6748 ThanksDenis

Hi @MA1985_CG Yes this is a known topic (which is not new if you put yourself in the Declared ID principle from previous Experience Cloud solution integration) which Adobe is working on a long-term solution. Meanwhile, there are workarounds available if need be.ThanksDenis.