Faces merge automatically in Photo 3.0

Hi

I am having problem with Photo merging me and my son in "People". I have tried to delete all faces in my sons profile and then add him again, I have tried to delete all faces and reindex all faces. No luck. After a while thousands of pictures on me winds up in my sons profile. I am in contact with Apple but they need to "talk to the technicians" and do not have a clue. Anyone?

I use an Imac late 2009 (on high Sierra) as main computer, an Ipad pro and an Iphone 8. The problem only seems to occur on the Imac. The other devices display me and my son correct.

Erik