Did you change your filter to include all logs?
I will confess that I was once embarrassed by a client because the feature didn't work as expected. We simulated several types of attacks and none were blocked.
We got to involve Meraki and it never worked as expected. So in short, the customer gave up on the product.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.