QuestDB cloud ILP connection error: Failed to read authentication challenge (timed out?): Resource temporarily unavailable (os error 11)

Question

I am following the code example from QuestDB and migrating my data from InfluxDB. I have files exported in ILP format, so I read and send them one by one using:

    try:
        with Sender(host, port, auth=auth, tls=True, auto_flush=4096) as sender:
            with open(in_file, "r") as input:
                lines = input.readlines()

           
                for index, line in enumerate(lines):
                    table, symbols, columns, timestamp_nano = read_line(line, index)
                    sender.row(table, symbols=symbols, columns=columns, at=timestamp_nano)

    except IngressError as e:
        sys.stderr.write(f"Fail: {e}\n")

But sometimes after sending many files successfully, my script fails to connect with

Failed to read authentication challenge (timed out?): Resource temporarily unavailable (os error 11)

What does error 11 mean? Is is the auth failure or network?