Поправил

GasStation/Repositories/Implementations/SellingRepository.cs

@@ -73,10 +73,10 @@ VALUES (@Id, @ProductID, @Count)";
             var querySelect = @$"
 SELECT
     s.*,
+    g.GasmanName,
     CONCAT(p.ProductType, ' ', p.ProductName) as ProductName,
     ps.ProductId,
-    ps.Count,
-    g.GasmanName
+    ps.Count
 FROM Selling s
 LEFT JOIN Gasman g on g.ID = s.GasmanID
 INNER JOIN Product_Selling ps ON ps.ID = s.ID
@@ -92,7 +92,7 @@ LEFT JOIN Product p on p.Id = ps.ProductID
                 }
                 ps.Add(sellings);
                 return sell;
-            }, splitOn: "ProductId", param: new
+            }, splitOn: "ProductName", param: new
             {dateTime, count, gasmanID});
             _logger.LogDebug("Полученные объекты: {json}",
             JsonConvert.SerializeObject(selling));