I’m seeing a similar issue on macOS 26.3.1. It doesn’t reproduce every time, but it tends to happen when calling SFContentBlockerManager.reloadContentBlocker twice with a ~2s delay: first reload loads large JSON (~9–11 MB) second reload updates rules to almost empty (~100 bytes) Both calls return success and files on disk look correct. But after the second reload Safari sometimes doesn’t call beginRequest for some blockers, and they keep using old rules. In my logs, these are the same blockers that loaded large JSON in the first reload. If I increase the delay between reloads, the issue mostly disappears.