After using the php function fwrite: extra dots inside the file when viewing online (not after downloaded)

I have a function that create a file using the function fwrite. I've noticed that after the file is created, if I open the file using the online file manager of my host, I can see an extra dot inside the file. I cannot see this dot when downloading the file on my computer (linux Mint) and viewing it.

This extra dot cause an Uncaught Error: Undefined constant "". When I remove the extra dot online everything works normally. I have no idea where this extra dot come from and why I cannot see it on my computer.

You can see on the pictures the problem same file viewed online and on my computer

Here is the code that generate the file: The file is on a subdomain folder and is generated from the main domain name.

//regenerate the spam list using the updated database
        $path_to_file = '/home/xxxxxxx/domains/xxxxxx.com/public_html/xxxxxxx/banned_words.php';
        $myfile = fopen($path_to_file, "w") or die("Unable to open file!");
        $txt1 = "<?php // The list of not allowed words\n\$not_allowed_words = [\n";
        $txt3 = "];?>";
        fwrite($myfile, $txt1);   
        // Query to fetch stories
        $stmt = $pdo->prepare('SELECT * FROM banned_words ORDER BY id ASC');
        $stmt->execute();
        $data = $stmt->fetchAll();
        foreach ($data as $row) { 
        $banned_word = $row["banned_word"];
        $txt2 = "    '".$banned_word."',\n";
        fwrite($myfile, $txt2);
        }
        fwrite($myfile, $txt3);

Thank you to anyone with an idea!

I tried to modify the file online (remove the extra dot) and it works I tried to download the file to modify it but when opening the file on my computer the extra dot does not appear I tried to modify the function but nothing worked

EDIT: I have the same problem when generating sitemap files in xml. I tried removing the <? tag to test but the extra character still appears

Problem resolved: I simply had to delete this line and type it again : $txt3 = "];?>";

Same problem with the sitemap files generator.