The Wordfence plugin tries to contact its remote API. The request stops before the server replies. The timeout triggers a cURL error 28 and Wordfence reports that the API rate limit was exceeded.
Root causes include blocked loopback traffic, low PHP curl timeout, server resource throttling, DNS lookup failures, SSL handshake problems, or hitting Wordfence’s own quota. When any of these conditions occur the outbound call never finishes, so Wordfence aborts with the error message.