This problem may be occurring for several reasons, such as a poorly planned network design, roaming issues due to client load balancing, Wi-Fi network card driver issues, etc.
Ideally, a site survey should be conducted, but here is a document that can guide you.
https://documentation.meraki.com/Wireless/Troubleshooting_and_Support/Troubleshooting/Wireless_Issue...
I also suggest you open a support case.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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