agent is locked if ssh process exits

There is no SSH process:
    1 3908 3889 2313 pts/0 8901 S 0 6:37 python /usr/bin/twindb --start
 3908 20577 3889 2313 pts/0 8901 S 0 0:11 \_ perl /usr/bin/innobackupex --stream=xbstream --user=twindb_agent --password=**** --socket=/var/lib/mysql/mysql.sock --slave-info --safe-slave-backup --safe-slave-backup-timeout=3600 . --defaults-extra-file=/tmp/tmptTDhGO
20577 20583 3889 2313 pts/0 8901 Sl 0 0:28 | \_ xtrabackup --defaults-extra-file=/tmp/tmptTDhGO --defaults-group=mysqld --backup --suspend-at-end --target-dir=/tmp --innodb_data_file_path=ibdata1:12M:autoextend --tmpdir=/tmp --extra-lsndir=/tmp --stream=xbstream
 3908 20578 3889 2313 pts/0 8901 SL 0 0:00 \_ gpg --homedir /root/.gnupg/ --encrypt --yes --batch --no-permission-warning --quiet --recipient e456b18e-11eb-49ff-93f9-5341656799fe

GPG write call is blocked:

[root@db-02-production ~]# strace -p 20578
Process 20578 attached
write(1, "\222g\\\215\\\330S\235^!\264C:\232\331\355@P\"\211\262|\321R\3660\321\361yce\232"..., 4096

# less /tmp/twindb.ssh.err
Connection closed by 54.174.107.234