As reported in T175725: Deploy HTML5 sections to WMF production, some characters are problematic when used in wikitext anchor-encoded with html5 set as primary mode in $wgFragentMode.
<ref name="[]"> is broken because Cite uses wikitext for link generation.There's T29694 for it.- Some links like [{{fullurl:{{PAGENAME}}}}#{{anchorencode:[]}}] don't work anymore.