Flushing file's with webkit's filesystem API with Safari

Question

I am trying to use filesystem api to create permanent files, write and read data from them. Although I succeeded creating the file and writing data to it, after calling flush() the file becomes empty (and it's size is 0). The files that I created exist and I can still see them in a different running of safari, but the data is lost and the file's are all 0 sized. Even if I try to read the file just after writing to it and flushing, the data is lost and it's size returns to 0. Does anybody know what I am doing wrong?

I tried running this:

console.log("Starting");
async function files() {

// Set a Message
const message = "Thank you for reading this.";
const fileName = "Draft.txt";

// Get handle to draft file
const root = await navigator.storage.getDirectory();
const draftHandle = await root.getFileHandle(fileName, { create: true });
console.log("File Name: ", fileName);
// Get sync access handle
const accessHandle = await draftHandle.createSyncAccessHandle();

// Get size of the file.
const fileSize = await accessHandle.getSize();
console.log("File Size: ", fileSize); // getting 0 here
// Read file content to a buffer.
const buffer = new DataView(new ArrayBuffer(fileSize));
const readBuffer = accessHandle.read(buffer, { at: 0 });
console.log("Read: ", readBuffer); // getting 0 here because the file was just created

// Write the message to the file.
const encoder = new TextEncoder();
const encodedMessage = encoder.encode(message);
const writeBuffer = accessHandle.write(encodedMessage, { at: readBuffer });
console.log("Write: ", writeBuffer); // writing 27 bytes here, succeeding

// Persist changes to disk.
accessHandle.flush();

// Always close FileSystemSyncAccessHandle if done.
accessHandle.close();
console.log("Closed file ");

// Find files under root/ and print their details.
for await (const handle of root.values()) {
    console.log('Item in root: ', handle.name);
    if (handle.kind == "file") {
        let f = await handle.getFile();
        console.log("File Details: ", f); // I can see here the file I created now and earlier created files, but all of them are 0 sized
        }
    }
}

files();