Have you tried changing the cable? Have you checked with your ISP to make sure the link is not unstable? Have you tested this link on any other device?
What version of MX are you running? Is this a new or old installation?
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.