As seen See root-forum.cern.ch/t/crashes-when-reading-a-ttree-with-a-friend/45543
and root-forum.cern.ch/t/a-crash-when-reading-from-a-file-with-ttree-friends/48388 there are case where the order of deletion of a TTree and its friend TTree lead to use-after-delete of some of the TFriendElement or other related element.