Please add filters for loss and latency discovery in Cisco Meraki device by HTTP template. There is no data from API about loss and latency checks when the device is down.
Here is the example of API response when the device is down:
{
   "networkId":"L_620933798623721683",
   "serial":"Q2LY-3H9V-J2AG",
   "uplink":null,
   "ip":null,
   "timeSeries":[
     

{          "ts":"2022-11-17T07:00:52Z",          "lossPercent":null,          "latencyMs":null       }

   ]
}

This filters needed:

• IP-address matches "((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4}$" and not matches "^$";
• uplink matches ".+" and not matches "^$".

Also please change preprocessing for loss and latency items. "Custom on fail" and set value to "-1" is needed in first step (jsonpath) to avoid unsupported items when the device is down. Javascript step is not needed in this case.