Cf. https://github.com/uber/jaeger/issues/310
When a user retrieves multiple traces, a single trace that doesn't exist (due to TTLing) will return an error for the entire batch. This has been fixed on the query side to return as many traces as possible + errors for the traces that couldn't be fetched.
Current version of the UI does not parse the errors portion of the response, it only seems to react to the status code.