5.6: Xtrabackup SST fails with xtrabackup version 2.4.20

[temeo]

+ set -e
+ [[ ! -s /var/lib/mysql//.sst/xtrabackup_checkpoints ]]
+ wsrep_log_error 'xtrabackup_checkpoints missing, failed innobackupex/SST on do
nor'
+ wsrep_log '[ERROR] xtrabackup_checkpoints missing, failed innobackupex/SST on 
donor'
++ date '+%Y%m%d %H:%M:%S.%N'
++ cut -b -21
+ local readonly 'tst=20200615 15:07:46.213'
+ echo 'WSREP_SST: [ERROR] xtrabackup_checkpoints missing, failed innobackupex/SST on donor (20200615 15:07:46.213)'
WSREP_SST: [ERROR] xtrabackup_checkpoints missing, failed innobackupex/SST on donor (20200615 15:07:46.213)
+ exit 2