The error below is displayed when updating the database. This issue was not there on version 2.66.0+170619.

Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '\'default\', created datetime not null, first_read datetime null ) ENGINE=' at line 9. The SQL statement executed was: CREATE TABLE ls_notifications ( id int(11) NOT NULL AUTO_INCREMENT PRIMARY KEY, entity varchar(15) not null, entity_id int(11) not null, title varchar(255) not null, message text not null, status varchar(15) not null default 'new' , importance int(11) default 1, display_class varchar(31) default \'default\', created datetime not null, first_read datetime null ) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

This issue is related to line 1564 in updatedb_helper.php.

On version 2.66.0+170619 it was:
'display_class' => 'string(31) default \'default\'',

On version 2.67.0+170622 the line has been changed, it leaves unwanted backslashes in the SQL query:
'display_class' => "string(31) default \'default\'",