BIGINT UNSIGNED VALUE IS out of range My SQL

Please read “Out-of-Range and Overflow Handling“.
It says:

As of MySQL 5.5.5, overflow during numeric expression evaluation results in an error. For example, the largest signed BIGINT value is 9223372036854775807, so the following expression produces an error.

mysql> SELECT 9223372036854775807 + 1;

ERROR 1690 (22003): BIGINT value is out of range in '(9223372036854775807 + 1)'

To enable the operation to succeed in this case, convert the value to unsigned;

mysql> SELECT CAST(9223372036854775807 AS UNSIGNED) + 1;
+-------------------------------------------+
| CAST(9223372036854775807 AS UNSIGNED) + 1 |
+-------------------------------------------+
|                       9223372036854775808 |
+-------------------------------------------+

A change to part of your query, as following, would solve the issue.

( CAST( quantity AS SIGNED ) - COUNT( game_moblist.spawn_id ) ) AS quantity_to_spawn

Otherwise you may require to change the sql_mode on unsigned operations.

mysql> SET sql_mode="NO_UNSIGNED_SUBTRACTION";

and then run your query to get desired output.

See also a similar posting answered on a forum here.