Notice: Unknown: Skipping numeric key 1 in Unknown on line 0

Notice: Unknown: Skipping numeric key 1 in Unknown on line 0

I have the following code:
include 'includes/connect.php';
$sp= "clot";
$selectall = mysqli_prepare($connection, "SELECT Count FROM prices WHERE
Category = ? ORDER BY ppu LIMIT 11");
mysqli_stmt_bind_param($selectall, 's', $sp);
mysqli_stmt_execute($selectall);
$resulttotal = mysqli_stmt_get_result($selectall);
$x=1;
while($row = mysqli_fetch_array($resulttotal, MYSQLI_ASSOC)){
$_SESSION[$x] = $row['Count'];
$x++;
}
$y=1;
while(isset($_SESSION[$y])){
if($y==11){
$_SESSION['nextstart'] = $_SESSION[$y];
unset($_SESSION[11]);
}
else{
echo($y);
echo("<br>");
echo($_SESSION[$y]);
echo("<br>");
$y++;
}
}
Which outputs the expected string of numbers (1, 17, 2, 18...) this error
message(ten times, with key 1, key 2, key 3, and so on):
Notice: Unknown: Skipping numeric key 1 in Unknown on line 0
Looking this error up, the only answer I could find was that putting an
array into a superglobal would cause this. I don't believe I've put an
array in, $row['Count'] is a string, isn't it? I couldn't find any entries
on stackoverflow about this error.
What causes this error, and what should I do to fix it? (The shown code is
just me experimenting and planning a design for endless pagination using
my database.)