pfSense

Impossibly high, or impossibly low?
Yes, I have seen occasions when the ping time is impossibly low for a while. I think it is after ping time has been unusually high for a while (genuinely - downloading big stuff on a slow link), and then goes back to "normal". The rolling average calculation in some way might be "overshooting" on the way back down to the new "average". It reported like 1ms, 2ms to 8.8.8.8. After 5 minutes or so it settled down to an expected sort of number, for me around 100ms.
I haven't done any real testing of that - I will try a few big download-stop download-observe RTT reports... cycles this evening and see if I can find a repeatable sequence.

To add: minimum possible WAN GATEWAY ping return value is 7ms (100% impossible for it to go under that number, a cable connection afterall, with an average at low load of 8-9ms) yet apinger is returning values of 0.5-4ms for the past 2 days. Also, during peak usage hours response times ALWAYS go up to an average of 20ms (as noted by daily logs for the past half decade), yet now they remain at 0.5-4ms running 2.2RELEASE.
Also of note (may be related as its using apinger), the system is no longer able to accurately track small outages (under a minute), and no logs are produced under system logs / gateways, as previously shown.