Why can’t I assign values to my $_SESSION variables?

I have a problem that for some reason my $_SESSION variables seem to be empty when I am trying to echo them onto the form you can see on the picture. The name field (‘Név’ on the picture) works, however it is from another table from my database.

Here are the corresponding PHP code snippets:

personal.inc.php:

<?php
    session_start();
    ini_set('display_errors', 1);
    ini_set('display_startup_errors', 1);
    error_reporting(E_ALL);

    require_once 'dbh.inc.php';
    require_once 'getpersonal.inc.php';


    if (isset($_POST["submit_personal"])) {
        $birthdate = $_POST["birthdate"];
        $bio = $_POST["bio"];
        $dailyTime = $_POST["chintime"];
        $favChin = $_POST["favchin"];
        $ownsChinchilla = $_POST["owns_chinchilla"];
        $loveTime = $_POST["year_selector"];
        $userID = $_SESSION["id"];
        $new_name = $_POST["name"];

        $nameUp = "UPDATE user_form SET name='$new_name' WHERE id='$userID'";
        $conn->query($nameUp);

        $checker = "SELECT COUNT(*) FROM personal WHERE userID = '$userID'";
        $result = mysqli_query($conn, $checker);
        $row = mysqli_fetch_array($result);

        if ($row[0] > 0) {
            $stmt = $conn->prepare("UPDATE personal SET bio = ?, birthDate = ?, dailyTime = ?, loveTime = ?, favChin = ?, owner = ? WHERE userID = ?");
            $stmt->bind_param("ssssssi", $bio, $birthdate, $dailyTime, $loveTime, $favChin, $ownsChinchilla, $userID);
        } else {
            $stmt = $conn->prepare("INSERT INTO personal (userID, bio, birthDate, dailyTime, loveTime, favChin, owner) VALUES (?, ?, ?, ?, ?, ?, ?)");
            $stmt->bind_param("issssss", $userID, $bio, $birthdate, $dailyTime, $loveTime, $favChin, $ownsChinchilla);
        }

        getPersonal($conn);

        $stmt->execute();

        $stmt->close();
        $conn->close();
    }

    header("location: user.php");
    exit();
?>

getpersonal.inc.php:

<?php
    require_once 'dbh.inc.php';

    function dataExists($conn, $userID) {
        $sql = "SELECT * FROM personal WHERE userID = ?;";
        $stmt = mysqli_stmt_init($conn);
        if (!mysqli_stmt_prepare($stmt, $sql)) {
            header("location: login.php?error=stmtfailed");
            exit();
        }

        mysqli_stmt_bind_param($stmt, "s", $userID);
        mysqli_stmt_execute($stmt);

        $resultData = mysqli_stmt_get_result($stmt);

        if ($row = mysqli_fetch_assoc($resultData)) {
            return $row;
        } else {
            $result = false;
        }

        mysqli_stmt_close($stmt);
        return $result;
    }

    function getPersonal($conn) {
        $dataExists = dataExists($conn, $_SESSION["id"]);

        $_SESSION["bio"] = $dataExists["bio"];
        $_SESSION["favChin"] = $dataExists["favChin"];
        $_SESSION["owner"] = $dataExists["owner"];
        $_SESSION["birthDate"] = $dataExists["birthDate"];
        $_SESSION["dailyTime"] = $dataExists["dailyTime"];
        $_SESSION["loveTime"] = $dataExists["loveTime"];
    }
?>

HTML

<form method="post" action="personal.inc.php">
                <label>
                    <div class="namer">
                        <span class="identifier">Név:</span>
                        <input class="inner" type="text" name="name" placeholder="Itt módosíthatod a neved..." value="<?php echo $_SESSION["name"];?>">
                    </div>
                </label>
                <label>
                    <div class=dob>
                        <span class="identifier">Születési idő:</span>
                        <br>
                            <input class="inner" type="date" name="birthdate" value="<?php echo $_SESSION["birthDate"];?>">
                    </div>
                </label>
                <label>
                    <div class="bio">
                        <span class="identifier">Bio:</span>
                            <textarea class="inner" name="bio" width=400px height=230px placeholder="Mesélj magadról, hogy jobban megismerhessünk..." value="<?php echo $_SESSION['bio'];?>"></textarea>
                    </div>
                    
                </label>
                <label>
                    <div class=daily>
                        <span class="identifier">Napi csincsillával töltött idő:</span>
                        <br>
                        <select name="chintime" class="inner" value="<?php echo $_SESSION["dailyTime"];?>">
                            <option>Nincs csincsillám</option>
                            <option>Kevesebb, mint 1 óra</option>
                            <option>1-2 óra</option>
                            <option>3-5 óra</option>
                            <option>Több, mint 5 óra</option>
                        </select>
                    </div>
                </label>
                <label>
                    <div class="fav">
                        <span class="identifier">Kedvenc csincsilla a boltunkból:</span>
                        <div class=inner>
                            <select name="favchin" value="<?php echo $_SESSION["favChin"];?>">
                                <option>Mindet imádom!</option>
                                <option>Puffancs</option>
                                <option>Kókusz</option>
                                <option>Hamu</option>
                                <option>Nutella</option>
                                <option>Mochi</option>
                            </select>
                        </div>
                    </div>
                    
                </label>
                <label>
                    <div class="owner">
                        <span class="identifier">Van csincsillád?</span>
                        <div class=inner>
                            <select name="owns_chinchilla" value="<?php echo $_SESSION["owner"];?>">
                                <option>Nincs</option>
                                <option>Van</option>
                            </select>
                        </div>
                    </div>
                </label>
                <label>
                    <div class="longlove">
                        <span class="identifier">Mióta imádod a csincsillákat?</span>
                        <br>
                            <input class="inner" type="number" name="year_selector" id="year_selector" min="1900" max="2099" step="1" value="<?php echo $_SESSION["loveTime"];?>">
                    </div>
                </label>
                <button class="savebtn" type="submit" name="submit_personal"><i class="fa-solid fa-floppy-disk"></i><span>Mentés</span></button>
            </form>

This is what I expreience right now:
https://i.stack.imgur.com/tbHQI.png

I would like to echo the $_SESSION variables into my form when they are set in my database, so if the user only updates 1 field, the other fields won’t be touched.

Any form of help is appreciated,

Blaise