I don't believe it's an STP problem, can you at least access the switch's local status page?
Can you validate if the Switch received an IP (if it doesn't have a static IP)?
You must first check the integrity of your network, if you have a firewall on the network, check that it is not blocking communication with the Meraki cloud.
Otherwise 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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