When is a 'message' blocking or not for the dashboard UI?

[ChrisNolan]

I was noticing (when working on #1095) that the dashboard UI, if it gets a 'message' it doesn't show the rate results -- or any details about the error. When I dig into the api logs I see that it is flagged as a 'warn' severity and still gives the rates anyway but the UI blocks that.

Is this a fedex specific thing, or more generic? What would be the best way to handle this?

e.g.

UI shows error

fedex We are unable to process this request. Please try again later or contact FedEx Customer Service.

API logs show

  "messages": [
    {
      "message": "We are unable to process this request. Please try again later or contact FedEx Customer Service.",
      "code": "MIXED.MEASURING.UNITS.INCLUDED",
      "level": "warning",
      "details": {},
      "carrier_name": "fedex",
      "carrier_id": "fedex-lerner-test"
    }
  ],