We encountered this issue on a large deployment running 11.22, were advised by Meraki to upgrade to 11.30 - we are still encountering the issue. Meraki stated it is triggered by a STP TCN. Hard reboot is the temporary workaround, which is an issue when it is a core stack. Meraki confirmed it is a known bug with 11.30, that a fix is in progress but no ETA as yet. We are now planning to break the stack for a single switch to provide L3 to provide a workaround that doesn't involve rebooting the core, or alternatively to move L3 to another non-Meraki device.
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