Microsoft asked me to change the SLO logout URL (Meraki Dashboard>Organization>Settings>Authentication) to the following: https://login.microsoftonline.com/common/wsfederation?wa=wsignout1.0 That resolved the sign out error for us. As an aside, we access the Meraki dashboard via an Incognito window, so there are no other unintended SSO logouts when using the SLO Logout URL.
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