If you capture on the MX LAN side you should have each packet twice in the capture. Once with the source MAC address of the device in VLAN 60 and the MX as destination. And the second time with the MAC address of the MX as source and the windows/printer device in VLAN 70. If you see those packets twice, then the MX is forwarding correctly and you are experiencing issues on the switched network or on the end hosts.
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