Consider this wikitext:
Foo {{refn|group="note2"|Foo-ref <ref>abcd</ref>}}
Bar {{refn|group="note2"|name="Bar-name"|Bar-ref.<ref name="Bar-name">pqrs</ref>}}
<references group="note2" />Parsoid's HTML doesn't include the nested ref for Bar and instead leaves behind this: <sup typeof="mw:DOMFragment/sealed/ref" id="mwMg" data-mw="{"name":"ref","attrs":{"name":"Bar-name"},"body":{"extsrc":"pqrs"}}"></sup>. That should have been properly processed in Cite and replaced with the right sup-tag with the nested ref content.
Not sure if this has always been broken or broken recently, but needs fixing.
But, https://en.wikipedia.org/w/index.php?title=User:SSastry_(WMF)/sandbox&oldid=1278679014 has a test case on wiki.
The actual page where I found this error was https://en.wikipedia.org/wiki/2020_BWF_World_Tour which is one of the pages throwing the convert-offsets error in rt-testing (only in some special circumstances, not always, as it turns out).