Meanwhile, I've tested with 6.0.1 and there we have the same issue:
Jul 18 10:12:37 ttel /usr/sbin/kamailio[40902]: NOTICE: {1 32 BYE 395608307-5062-4@BA.A.B.BCJ} <core> [core/kemi.c:157]: sr_kemi_core_log(): ksr_branch_manage: 1 Jul 18 10:12:37 ttel /usr/sbin/kamailio[40902]: ERROR: {1 32 BYE 395608307-5062-4@BA.A.B.BCJ} pv_headers [pvh_xavp.c:487]: pvh_clone_branch_xavi(): cannot clone xavi from non existing parsed_pv_headers Jul 18 10:12:37 ttel /usr/sbin/kamailio[40902]: NOTICE: {1 32 BYE 395608307-5062-4@BA.A.B.BCJ} <core> [core/kemi.c:157]: sr_kemi_core_log(): ksr_branch_manage: 2: 200102 Jul 18 10:12:37 ttel /usr/sbin/kamailio[40902]: NOTICE: {1 32 BYE 395608307-5062-4@BA.A.B.BCJ} <core> [core/kemi.c:157]: sr_kemi_core_log(): ksr_branch_manage: 3: 200102