Sphinx Search Fails with Error: "connection unexpectedly closed (timed out?)"

I am a total beginner at this, so please forgive me if this is a dumb question.

I am using the "sphinxapi.php" API to search through about 400,000 WordPress posts.

Some search terms always succeed (e.g. "wheelbarrow" or "employee") but others always
fail (e.g. "worker" or "wood"). All terms are included in the documents.

When the search fails, a PHP error is thrown:

<b>Notice</b>: fwrite(): send of 8192 bytes failed with errno=104 Connection reset by
peer in
<b>/home/caselaw/domains/dev.caselaw.tk/public_html/wp-content/plugins/caselaw/sphinxapi.p
hp</b> on line <b>486</b>

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Around line 486 in sphinxapi.php is the following code (starting line 485):

function _Send($handle, $data, $length) {
        if (feof($handle) || fwrite($handle, $data, $length) !== $length) {
            $this->_error = 'connection unexpectedly closed (timed out?)';
            $this->_connerror = true;
            return false;
        }
        return true;
    }

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How can I even start finding out what is going on?

My dev site is at http://dev.caselaw.tk/search-page/. I am trying to get simple
searches work first, without using the Courts, Categories and Ratings filters on the form.