Can't think why at all ... try a bit of debugging (if you haven't already) ...
<?php
$viewss = file("counterlog.txt");
echo '<hr>Whole file:<br><pre>'.join('', $viewss).'</pre><hr>';
$views = $viewss[0];
echo '<hr>First line:<br><pre>'.join('', $views).'</pre><hr>';
$views++;
echo '<hr>After inc:<br><pre>'.join('', $views).'</pre><hr>';
$fp = fopen("counterlog.txt", "w");
fwrite($fp, $views);
fclose($fp);
?>
See how that goes ...
Paul 🙂