Cannot use $exists, returned "Error: Invalid object id : 'false'"

I'm having a fatal problem very much when about the ACS.

I tried the simple query, below.

Cloud.Places.query({
    where: {
        abc_id: { "$exists" : false }
    }
},
function (e) {
    alert(e);
});

I think, cannot use "$exists" when custom field name contains '_id'. I tried change abc_id to def_id and xyz_id... But it has same problem. Is not only on "Places", there is a problem on "Users".

But my released applications are using these fields, because my applications are down...I am very troubled.

It was working correctly a week ago. The ACS has the problem now?