Invalid progress data from server
Remote URL import was streaming progress, but one line from the server was not valid progress JSON.
Why this happens
POST /api/upload/from-url should send NDJSON: one JSON object per line with a type such as progress, done, or error. The browser throws this when a line fails to parse — often HTML from a proxy error page, a truncated body, or middleware that injected non-JSON into the stream.
This is different from Empty response body (no stream at all) and from Import finished but no file id returned (stream ended without a done file id).
Diagnose and fix
1. Reproduce on Upload → Remote URL. In DevTools → Network, open the from-url response — lines should be JSON, not HTML.
2. Fix reverse-proxy buffering/timeouts on that path; do not replace the stream with an error document mid-transfer.
3. Confirm Mods → Remote URL upload is on and the tier is not blocked (toggle.ul2_remote_url_* — on means blocked).
4. Retry a small direct https:// URL. If every import fails the same way, check app and proxy logs for that request.