I am looking at couple of docs
The first blog mentions that backup locks are preferable to FTWRL.
However, doc on limitations mentions
“”" Backup locks used during SST or with Xtrabackup can crash, on donor, either use inno-backup-opts=’–no-backup-locks’ under [sst] in my.cnf or set FORCE_FTWRL=1 in /etc/sysconfig/mysql (or /etc/sysconfig/mysql.%i for corresponding unit/service) for CentOS/RHEL or /etc/default/mysql in debian/ubuntu. You can also use rsync as the alternate SST method if those don’t work. “”"
Is this still a limitation? If so, does it happen often under heavy load?