EX VLAN loop (purposeful) not passing traffic..

New to Junos here, so please be kind!  

I have an EX4600 that I'm configuring to link some downstream routers to (mikrotik). My requirement is that all incoming traffic from the downstream routers pass from the switch, to an external QoS Server (layer 2) and back into the switch. I've separated out the incoming traffic on vlan 120 to keep the traffic segragated. 

If I add an l3-interface to vlan120, I can then ping 10.0.0.11, but also lets the traffic directly access 10.0.0.11 without going through the QoS server. I suspect it's an ARP port-learning issue or something. My knowledge of layer 2 switching is being taxed. :/ 

Here is my setup: 

version 18.1R3.3;
groups {
  global;
}
interfaces {
  xe-0/0/8 {
    unit 0 {
      family ethernet-switching {
        interface-mode access;
        vlan {
          members queue120;
        }
      }
    }
  }
  xe-0/0/9 {
    unit 0 {
      family ethernet-switching {
     interface-mode access;
        vlan {
          members queue120;
        }
      }
    }
  }

  xe-0/0/12 {
    unit 0 {
      family ethernet-switching {
        interface-mode access;
        vlan {
          members queue110;
        }
      }
    }
  }
  xe-0/0/13 {
    unit 0 {
      family ethernet-switching {
        interface-mode access;
        vlan {
          members queue120;
        }
      }
    }
  }
  irb {
    unit 0 {
      family inet {
        dhcp {
          vendor-id Juniper-ex4600;
        }
      }
    }
    unit 110 {
      family inet {
        address 10.0.0.11/24;
      }
    }
  }
  lo0 {
    unit 0 {
      family inet;
    }
  }
}
forwarding-options {
  storm-control-profiles default {
    all;
  }
}
routing-options {
  router-id 10.0.0.11;
}
protocols {
  rstp {
    interface xe-0/0/12 {
      disable;
    }
    interface xe-0/0/13 {
      disable;
    }
    interface all;
  }
}
vlans {
  default {
    vlan-id 1;
    l3-interface irb.0;
  }
  queue110 {
    description "EX -> Q -> Towers";
    vlan-id 110;
    l3-interface irb.110;
  }
  queue120 {
    description "Towers -> Q -> EX";
    vlan-id 120;
  }
}

I disabled RSTP on interfaces 12 and 13 as though those are technically a loop, I figured having them access ports for different vlans would supress any storms, etc. 

Any ideas as to why I can't access layer 3 traffic through the loop? Could it be that R1 / R2 learn of the mac of 10.0.0.11 which isn't on the interface they're connected through? 

EDIT: for simplicity, I've tried putting in a simple switch in place of the QoS server, and even a literal loop. No change.