OS Error 11 (EAGAIN) from inside TLS about ureq HOT 5 CLOSED

pub fn fetch_capabilities(
    client: &HttpClient,
    cap_url: &str,
    keys: &[&str],
) -> Result<HashMap<String, String>, Error> {
    const RETRIES: usize = 0; // try this many times
                              
    //  Construct request in LLSD format
    let query = compose_query(keys).with_context(|| {
        format!(
            "Composing query for capabilities {:?} from {}",
            keys, cap_url
        )
    })?;
    //  Retry query. Especially on Open Simulator, tries can fail.
    //  Documentation says that firewall/CDN problems can cause transient 5xx errors.
    let mut try_count = 0;
    let reply = loop {
        log::info!("Capability query to {}: {}", cap_url, query);
        //  Send HTTP request and block.
        let http_result = client
            .agent
            .post(cap_url)
            ////.set("Content-Type", "text/xml") // "text/xml; charset=utf-8" is rejected by SL server
            .set("Content-Type", "application/llsd+xml") // "text/xml; charset=utf-8" is rejected by SL server
            .send_string(&query)
            .map_err(anyhow::Error::msg)
            .with_context(|| format!("Fetching capabilities {:?} from {}", keys, cap_url));
        //  Analyze result
        match http_result {
            Ok(reply) => break reply, // good
            Err(e) => {
                log::error!(
                    "Error reading capability {}, try {}: {:?}",
                    cap_url,
                    try_count,
                    e
                );
                try_count += 1;
                if try_count > RETRIES {
                    return Err(e);
                }
                std::thread::sleep(std::time::Duration::from_millis(1000)); // wait before retry
            }
        }
    };
   ...