See CORE-1864 I believe you are affected by this. A fix has been implemented for 3.6.1, and I'm including the hotfix here if you'd like to manually resolve it on your system in the interim.
In /plugins/billing_overview/models/billing_overview_statistics.php update lines 44 and 45
FROM:
$this->Record->innerJoin("transaction_types", "transaction_types.id", "=", "transactions.transaction_type_id", false)->
where("transaction_types.type", "=", "debit");
TO:
$this->Record->on("transaction_types.type", "=", "debit")->
leftJoin("transaction_types", "transaction_types.id", "=", "transactions.transaction_type_id", false);
In /plugins/billing_overview/models/billing_overview_plugin.php update line 16
FROM:
private static $version = "1.3.0";
TO:
private static $version = "1.3.1";