Ajax callback and wrappers on unlimited fields(multifield)

One thing to take note when using ajax callbacks on filed that can have unlimited number is to use delta in wrapper names.

      '#ajax' => [
        'callback' => [$this, 'fetchLinkData'], 
        'disable-refocus' => FALSE, 
        'event' => 'change',
        'wrapper' => 'content-wrapper-' . $delta, 

you should have this added as wrapper and then also when setting this wrapper in formElement or formBuild is to have id added to div

      '#prefix' => '<div id="content-wrapper-' . $delta . '">',
      '#suffix' => '</div>'