One remaining hypothesis for the long-term decline in KaiOS web traffic is that KaiOS is still being widely used, but some type of proxy is preventing its pageviews from being counted in traffic statistics (both our and those of Statcounter and Device Atlas).
Our leading candidate is currently Google Web Light, although it's not clear what evidence it leaves on our servers when it's used. Google's page states: "the Web Light user agent is used only for explicit browse requests of a human visitor, and so it can ignore robots.txt rules", which suggests that Google does make server-side requests corresponding to client requests. However, it might be that after a first request for a page, requests from other users for the same page are cached, so we still can't get a full picture of Google Web Light use.