The updated reference working hypothesis is that the symptomatic NSS for some reason did not consistently initialize itself, possibly with the owner's WebID using WebID-OIDC protocol when installed. Apart from this, preliminary analysis revealed that the culprit variable (alternatively) could be a flaw in symptomatic NSS scripts involved in dynamically reading out pages index.html. Anyway, take note of the favicon.ico read out as expected and displayed in the upper left corner of the web browser's window.
With full details cf. Section Initial Access Authorization presented on an intermittently with intermediate interruptions, as a general rule between 20:00 and 07:00 GMT/UTC o'clock, and temporarily operated web server.