It appears that fix for bug
MDEV-20225 was fixed only in 10.4 version. The related test did not show problems with 10.3 and 10.2, at least. It may be that 10.1 was not tested at the time of MDEV-20225 preparation. However, running the related mtr test galera.galera_sp_bf_abort in current 10.1 HEAD revision, causes assert failure.
The conclusion is that
MDEV-20225 should be backported to 10.1 and 10.2 and 10.3 should be retested to verify if there is some later work in earlier versions, which makes SP handling vulnerable.