Yes, you are probably allowing all traffic to the MX status page, this could influence it, because if I'm not mistaken it responds to both port 80 and 443.
It's a bit bizarre, but I've seen similar problems before.
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.