i added the following code to my comments.php:

    paginate_comments_links( array(
                'prev_text'  => '« précédent',
                'next_text' => 'récent »',
                'add_fragment'=> '#comments'
                ) );

when clicking the paging links the whole page shifts by 12px. A portion at the top is cut off and a portion is added below the footer. My html is contained by a #main div. I tried the following CSS approach:

#main:before { 
  display: block; 
  content: " "; 
  margin-top: 0;
  visibility: hidden; 
}

or

#main {
 scroll-margin-top: 0;
}

This has no effect. I tried various elements on my page with the same css, but nothing held the page in position and the shift is always happening. Only when i leave add_fragment empty (”) the page does not shift. But the focus is not on the comments.
Most likely this is a html problem. Has someone had a similar shift of the page, when the comments page links are clicked? Thanks for your suggestions. Theo