non-matching rule fires randomly and results in infinite-loop

The issue happens with specific problematic rule like below.
~~~
rule "Rule_174"
when
$fact : Fact(
pattern == "PatternA",
$itemList : itemList
)
$item : Item(
flag == null,
$typeScore : typeScore
) from $itemList

$record : Record(
key == $fact.key,
specialHandlingFlag != null,
decompScore == null,
type == $item.type
)
not Record(
this != $record,
key == $fact.key,
specialHandlingFlag != null,
decompScore == null,
type == $item.type
)
then
System.out.println("[DEBUG] before $fact=" + $fact + ", $item=" + $item + ", $record=" + $record);

modify($record)

modify($item)

modify($fact)

System.out.println("[DEBUG] after $fact=" + $fact + ", $item=" + $item + ", $record=" + $record);

end
~~~

In this rule, regarding $item fact taken from 'from' operator, flag is set to "1" in RHS .
But the same fact still match this rule continuously even if 2nd condition does not match(i.e. flag == null). This does not happen always but surely happens randomly.