Error during the backup a user

Hi,

When I want to create backup for a user account I encounter this error

RoundCube Backup Error:
Warning: mysqli::__construct(): (HY000/2002): No such file or directory in /usr/local/directadmin/scripts/backup_roundcube.php on line 121
Failed to connect to MySQL: (2002) No such file or directory


this is the line 121

$mysqli = new mysqli($mysql_host, $mysql_user, $mysql_pass);

Is MySQL running?
Is something on err log?

Everything was working fine. Yesterday I updated Apache and some other components to the latest version and then the error occured
I tried to build Roundcube several times but the error still occurs.
Right now MariaDB is running on this server. RoundCube DB is not empty. I can can use Roundcube to check my emails. The backup file is created. In Directadmin Task Queue there is only the following error:

2019:08:19-01:22:02: RoundCube Backup Error (3):
Warning: mysqli::__construct(): (HY000/2002): No such file or directory in /usr/local/directadmin/scripts/backup_roundcube.php on line 121
Failed to connect to MySQL: (2002) No such file or directory

Just install PHP 7.4 if you run MySQL8. Earlier versions of PHP aren't fully compatible with MySQL8 authentication methods.