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>'