Undefined variable

Hello !
I’m using successfully your plugin in several websites, but I have a problem with one of them … When i go to the “hnow my ranking” report, i get this error message :
Notice: Undefined variable: label in /home/mywebsite database/www/wp-content/plugins/google-rank-tracker/includes/KnowMyRankingsAdmin.php on line 867
this message displays under each keyword I asked to check, and results are not showing, it just keeps searching infinitely.

Here is the part of the code that is in cause :

public function position( $keyword ) {

			if ( isset ( $keyword['last_7day'] ) && $keyword['last_7day'] != 0 ) {

				$position = $keyword['last_7day'] - $keyword['current_rank'];

				if ( $position > 0 ) {
					$class = "up";
					$label = "Up $position";
				}
				if ( $position < 0 ) {
					$class = "down";
					$label = "Down " . abs( $position );
				}
				if ( $position == 0 ) {
					$label = "No change";
				}

				echo "<div class=\"position $class\">
					<span class=\"triangle\"></span>
					<span class=\"desc\">$label</span> "
					.__( "since last week", "know-my-rankings" ).
				"</div>";
			}
			else
				echo "<div class=\"position\">
					<span class=\"desc\">$label</span>&nbsp;</div>";
		}

The 867 line is the last one :
<span class=\"desc\">$label</span>&nbsp;</div>";

Do you have an idea what the problem could be ? thanks

https://wordpress.org/plugins/google-rank-tracker/