Cannot get the number of rows and fetch when using MySQLi prepared statement

I want to get the number of rows from the database, but when I try to do this the $g_check variable will be equal to 0 and my code will echo the $sugg_title message which is in the else statement. But in the database there are 4 inserted groups so the num_rows property should return 4.

$sql = "SELECT DISTINCT gp.logo, gp.name
        FROM gmembers AS gm
        LEFT JOIN groups AS gp ON gp.name = gm.gname
        WHERE gp.creator != ? AND gm.mname != ? LIMIT 10";
$stmt = $conn->prepare($sql);
$stmt->bind_param('ss',$log_username,$log_username);
$stmt->execute();
$g_check = $stmt->num_rows;
if ($g_check > 0){
  $result = $stmt->get_result();
  while ($row = $result->fetch_assoc()) {
    $agList .= '<a href="group.php?g='.$row["name"].'"><img class="group_margin" src="groups/'.$row["name"].'/'.$row["logo"].'" alt="'.$row["name"].'" title="'.$row["name"].'" width="70" height="70" /></a>';
  }
}else{
  $sugg_title = "You have no group suggestions at the moment. Click ";
  $sugg_title .= '<a href="all_groups.php">here</a> to view all groups.';
}

I put the strore_result() and the fetch() functions after execute() but then I get this error message: "Fatal error: Uncaught Error: Call to a member function fetch_assoc() on boolean"