metric name "navigationTiming" data abnormal

Negative number in value

{
    "fetchTime": -6,
    "workerTime": 0,
    "totalTime": -78,
    "downloadTime": -89,
    "timeToFirstByte": 11,
    "headerSize": -18446744073709552000,
    "dnsLookupTime": 4,
    "redirectTime": 0
}

fetchTime、totalTime、downloadTime、headerSize  why?
