A very simple MD file named Title is converted to this HTML (I removed all unrelated stuff):
<html dir="auto" lang="de">
<head>
<title>Titel</title>
<meta name="generator" content="DEVONthink 4.3.2"/>
<style>
…
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Untitled Document</title>
So, there are two title elements in the head section, and the second one is not even correct. That goes against the HTML standard which allows only one title in the head element.
Also, I suggest changing the order of elements so that all meta elements come before the (correct) title and the style comes last. This is of course only cosmetics but it makes for easier understanding when looking directly at the HTML.