Comment 2 for bug 1641745

General reproduce path:

1. Initialize/start PS 5.7.15 with innodb_page_size=64k + keyring plugin
2. Create tables using sysbench:
sysbench --test=/usr/share/doc/sysbench//tests/db/parallel_prepare.lua --mysql-socket=/tmp/mysql.sock --mysql-user=root --oltp-tables-count=16 --oltp-table-size=100000 --num-threads=8 --mysql-table-engine=innodb run
3.
alter table sbtest.sbtest1 compression='lz4';
alter table sbtest.sbtest2 compression='lz4';
alter table sbtest.sbtest3 compression='lz4';
alter table sbtest.sbtest4 compression='lz4';
alter table sbtest.sbtest5 compression='lz4';

optimize table sbtest.sbtest1;
optimize table sbtest.sbtest2;
optimize table sbtest.sbtest3;
optimize table sbtest.sbtest4;
optimize table sbtest.sbtest5;

alter table sbtest.sbtest1 encryption='Y';
alter table sbtest.sbtest2 encryption='Y';
alter table sbtest.sbtest3 encryption='Y';
alter table sbtest.sbtest4 encryption='Y';
alter table sbtest.sbtest5 encryption='Y';

4.
Running sysbench:
sysbench --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-socket=/tmp/mysql.sock --mysql-user=root --oltp-tables-count=16 --oltp-table-size=100000 --num-threads=2 --mysql-table-engine=innodb --max-time=0 --max-requests=0 --percentile=99 --report-interval=30 run

5. Try to backup:
xtrabackup --defaults-file=/mnt/workspace/PTB-run-percona-server-5.7-pxb-2.4.4/BTYPE/release/Host/centos7-64/mnt/var/ps_5.7.15_sysbench/test-0/mysql.1/my.cnf --no-timestamp --tmpdir=/mnt/workspace/PTB-run-percona-server-5.7-pxb-2.4.4/BTYPE/release/Host/centos7-64/mnt/var/ps_5.7.15_sysbench/test-0 --parallel=1 --target-dir=/mnt/workspace/PTB-run-percona-server-5.7-pxb-2.4.4/BTYPE/release/Host/centos7-64/mnt/var/ps_5.7.15_sysbench/test-0/backup-0.0 --keyring-file-data=/mnt/workspace/PTB-run-percona-server-5.7-pxb-2.4.4/BTYPE/release/Host/centos7-64/mnt/var/ps_5.7.15_sysbench/test-0/mysql.1/data/keyring --backup