Where clause does not work in group by query builder

Hi, the query works fine without where clause, but currently it returns empty result

return DB::table('orders')
         ->select(
             DB::Raw('COUNT(orders.id) as order_count'),
             DB::Raw('DATE(orders.created_at) day')
        )
        ->where('created_at','>' , Carbon::parse($request->start))
        ->where('created_at ','<' ,Carbon::parse($request->end))
        ->groupBy('day')
        ->orderBy('orders.created_at')
        ->get();

toSql() result :

select COUNT(orders.id) as order_count, DATE(orders.created_at) day from "orders" where "created_at" > ? and "created_at " < ? group by "day" order by "orders"."created_at" asc

here is what the dates look like:

dd(Carbon::parse($request->start)); 

Outputs:

Carbon\Carbon @1538352000 {#1291
  date: 2018-10-01 00:00:00.0 UTC (+00:00)
} 

EDIT:

If I have only one where or two where clause where both operators are greater ">" I get the results from db:

    ->where('created_at','>' , Carbon::parse($request->start))
    ->where('created_at ','>' ,Carbon::parse($request->end))