php password and user doesn’t after a new post call [closed]

I created a simple log-in form in php to access an archive with user and password (encrypted in MD5 without hash or salt).
I then decided to insert a filter in the archive page (to filter only results of a specific date).
When I run the filter the page no longer finds the user and password pair and redirects me to the login page.
The file is Archivio.php

Code without filter:

<?php
$utente = $_POST["Utente"];
$password = $_POST["Password"];
$password = md5($password);

$id=
$sql=mysqli_query($mysqli, "select * from Utenti_Archivio where Utente='".$utente."' and          Password='".$password."'");
    if (mysqli_num_rows($sql) == 1){
    }
    else{
        header( "Location: Login.html" );
        die;
    }

$querySQL = mysqli_query($mysqli, "select Nome,Cognome,Ospitante,Sede,`Ora entrata`,`Ora uscita`,Giorno from  `Archivio`");
?>

Code with filter:

 <div class="filtro">
            <form method="POST">
                <div class="textfiltro">
                    Filtra per giorno:
                </div>
                <div class="field">
                    <input type="text" name="data" id="data">
                </div>   
                <div>
                    <button class="filtrobutton">FILTRA</button>
                </div>        
            </form>
        </div>
<?php
$utente = $_POST["Utente"];
$password = $_POST["Password"];
$password = md5($password);

$id=
$sql=mysqli_query($mysqli, "select * from Utenti_Archivio where Utente='".$utente."' and          Password='".$password."'");
    if (mysqli_num_rows($sql) == 1){
    }
    else{
        header( "Location: Login.html" );
        die;
    }

$data = $_POST["data"];
if (!empty($data)) {
    $querySQL = mysqli_query($mysqli, "SELECT Nome,Cognome,Ospitante,Sede,`Ora entrata`,`Ora uscita`,Giorno FROM `Archivio` WHERE Giorno = '$data'");
} else {
    $querySQL = mysqli_query($mysqli, "SELECT Nome,Cognome,Ospitante,Sede,`Ora entrata`,`Ora uscita`,Giorno FROM `Archivio`");
}
?>

   <body>
      <div class="login-form">
         <form id="host" action="Archivio.php" method="post">
            <div class="field">
               <input type="text" name="Utente" placeholder="Utente" required>
            </div>
            <div class="field">
               <input type="password" name="Password" placeholder="Password" required>   
            </div>
            <button type="submit">ENTRA</button>
         </form>
         <button onclick="document.location='Home.html'">INDIETRO</button>
         <button onclick="location.reload()">RIPRISTINA</button>
      </div>
    </body>

Can you help me?

I have tried moving the credential verification query after the filter and using the get method for the filter but it does not solve the problem.