Looks like the bug was in a monkey-patched `window.fetch` https://github.com/PostHog/posthog-js/blob/759829c67fcb8720f... The biggest lesson here is, if you're writing a popular library that monkey-patches global functions, it needs to be really well tested. There's a difference between "I'll throw posthog calls in a try/catch just in case" and "With posthog I literally can't make fetch() calls with POST"
eg heap analytics still (as of this month) bad touches something inside hotwire and randomly entirely breaks hotwire causing every click to do a full page load. ime, it affects 30-60% of page loads. You can fix it (but thanks for 50+ hours of debugging) but making heap load after all hotwire js.