When you open up the route table for your Spoke/Branch and set it to Sort By: Priority as shown in the screenshot below.
Is the default route with the type Meraki VPN: VLAN, above the default WAN route? It should be.
Then, if it is, is the icon status showing a green circle? In my screenshot it's showing the revolving wheel icon which basically means that the needed tunnel is not yet established or not working, so it would fall back to the default WAN route.
If it is green then all packets should be routed over the VPN. If not we'll have to troubleshoot further.