"You need to increase the vlan-limit to be able to match or pop multiple VLAN tags. Otherwise the second tag is parsed as the Ethertype."
e.g.
# ovs-vsctl set Open_vSwitch . other_config:vlan-limit=2
and specify vlan mode for your port:
ovs-vsctl set port vhu0fd9ab54-39 vlan_mode=dot1q-tunnel tag=5