I just had this same issue plaguing me for a few weeks. Had multiple Cisco and AWS support engineers troubleshoot with me and we could not figure it out until this morning. I wanted to post a more specific solution in case others like me find this and start tearing their hair out: If you want your EC2 instance to be able to SSH to an on-prem device through Meraki, you need to add an inbound rule to your vMX's security group that allows SSH traffic from the VPC CIDR (or from whatever subnet/individual IP from that block). There are autogenerated rules from creating a vMX in AWS and SSH is not one of the protocols included because Meraki does not allow SSH into itself (so there would be no need for it in general).
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