I ran the same query you are trying to alert on in the Query Builder, though I changed from Sum to Latest, and as you can see, the most recent data is not 0s, it is NULLs.
The Alerts evaluator requires a numeric value to evaluate on, and NULLs do not equal 0s in this evaluation.
As far as I can see, this metric has only come in once in the past month, as you can see here:
So, an alert condition targeting when this value drops to zero will not work. Since the value is not hitting Zero, instead it is NULL, it will not be evaluated in the way you may expect. But also, it seems like even if this value did drop to zero, the condition would always be in violation, since there is only one spike above zero, everything else would be considered zero and so this condition would rarely come out of violation.
Can you clarify further what your goals are for this alert. Perhaps we can advise you on alternate set ups to hit your goals, as I don’t think the condition in it’s current form will help.