A lot of stuff to go through here. Need more information. First, remove the direct connections between your MX250 if that is what the lines between them is. That is not a supported configuration. Second, why do you need the WAN switches? Third, what are you trying to achieve with LAN and Internet interfaces connected to the WAN switches? The MX does not partisipate in STP, but it does forwards BPDUs. This article also might help you out 🙂 https://documentation.meraki.com/MX/Networks_and_Routing/MX_Layer_2_Functionality
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