Can't resolve time.nist.gov
The popular NTP server time.nist.gov is having DNS problems, at least from our vantage point on the US east coast. For us, this has meant that regularly scheduled security reports could not be sent, but there may be other consequences. Now is a good time to check your NTP settings and designate redundant time servers.
1 thread
Try http://time.gov
Thanks, indeed, there are many alternative NTP servers [1]. But I believe time.nist.gov is the default time server during Ubuntu installation, so there are many hosts that depend entirely on time.nist.gov.