Modern routers ship with filtering built in: time schedules, per-device pauses, content categories and app blocking. Once configured and forgotten, these settings produce faults that look nothing like a rule.
A blocked device usually connects to Wi-Fi normally and shows full signal, but every page times out or a specific app refuses to load. Because the connection itself is healthy, people rebuild the network instead of checking the rules.
Provider apps add another layer. Some mobile operators and broadband providers apply filtering in their own network, so the router looks clean while a category block sits upstream.
Diagnosing this is quick: test the same site on mobile data. If it loads there and not on Wi-Fi, the block is on the network, not the device.