It appears that mariabackup no longer updates xtrabackup_binlog_info file after completing prepare phase. The position in the file is therefore incorrect and can't be used to set up replication after a restore. The position reported in the prepare phase log is correct, it's just that the file is not updated.
This is critical as a lot of DBAs and tools use the content of this file to set up replication, manually or automatically. Please fix it ASAP!