Short answer: this error means a website’s Cloudflare check stopped the app before it could load anything. Update Mihon first — 0.21.2 specifically fixed logins failing with this message (for example Kitsu) — then open the source in Mihon’s WebView and complete the check manually once, so the app keeps the clearance cookie.
Why it happens
Sources and trackers sit behind Cloudflare, which challenges visitors it cannot verify. An app is not a full browser, so the challenge sometimes cannot complete automatically. Mihon’s 0.21.2 changelog lists the fix plainly: “Fixed Kitsu login failing with ‘Failed to bypass Cloudflare’.” The same release also fixed slowdowns when many requests hit a Cloudflare challenge at once — a burst of library updates can trigger exactly that.
The fixes, in order
- Update Mihon to 0.21.2+ from the official GitHub release (download page with file hashes). If your error is the Kitsu/tracker login one, this is the fix, full stop.
- Complete the check in WebView: open the failing source, choose Open in WebView from its menu, and solve the Cloudflare check like a human in a browser. Mihon keeps the resulting cookies, and the source usually works afterwards.
- Slow down bulk actions: if the error appears during a global library update, update in smaller batches per category instead of everything at once.
- Check your network path: some VPN exits, DNS filters and school/work networks are flagged aggressively by Cloudflare. Try a different network (or a reputable VPN, see VPN guide) to confirm the network is the trigger.
- Wait it out: repeated failed attempts can get your IP temporarily challenged harder. Give it an hour rather than hammering refresh.
What not to do
Do not install “Cloudflare bypass” extensions or APKs from forums — there is no such legitimate tool, and lookalike downloads are a common malware route. Do not change Mihon’s user agent to random strings found online; the default modern user agent works, and random strings often make challenges worse. Persistent 403s on a single source (rather than a Cloudflare page) are a different error: see HTTP 403 source errors.
Related: all troubleshooting guides · WebView login problems