People disappearing from my friend list

So as the title says people are disappearing from my friend list. This happens most frequently after I invite someone and he accepts, after that I log out, wait a bit and then log in again. The said friend is gone. With him we already had our discords so I could contact him that way and it turned out that he never unfriended me and that he didn't know what was happening too. After that he loged in and sent me a request. The other part is that after we unfriend (for the unknow reason) I could no longer send the said person a request. I can find it in the add friends or recently played games and click add friend but nothing would happen. I don't know how he sent me the request to add me again be he managed. I just find this really annoying bug and am asking if there is soloution to this bcs recently I encountered the same problem.

Thank you.