mariabackup hangs forever if using parallel threads

Issue was first noticed when upgraded MariaDB 10.4.21 => 10.4.22.
Verified now 10.4.26 behaves the same way.
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When running mariabackup in single threaded mode - no issue:

# mariabackup -u mysql -pxxx --backup --compress --compress-threads=1 --parallel=1 --stream=xbstream --extra-lsndir=/mysql_backup/ --target-dir=/mysql_backup/ --tmpdir=/tmp/database > /mysql_backup/d1.bkp 2> /tmp/e1.txt

=>
# ls -lha /mysql_backup/d1.bkp
rw-rr-. 1 root root 759M Oct 11 12:01 /mysql_backup/d1.bkp

When running mariabackup with 2 threads - hangs forever:

# mariabackup -u mysql -pxxx --backup --compress --compress-threads=2 --parallel=2 --stream=xbstream --extra-lsndir=/mysql_backup/ --target-dir=/mysql_backup/ --tmpdir=/tmp/database > /mysql_backup/d2.bkp 2> /tmp/e2.txt

Attached mariabackup logs from both single threaded (e1.txt) and 2-threaded (e2.txt) sessions.
Attached also gstack taken from hanging case - gstack_mariabackup_2_threads_hanging.txt