Addition or deletion of in references in source article while translation is on-going cause references in translation point to non-existing reference. It also cause publishing error because of this.
We found a case while debugging https://phabricator.wikimedia.org/T109255
While translating enwiki:ISKCON Temple Bangalore, somebody added a new reference to the source article https://en.wikipedia.org/w/index.php?title=ISKCON_Temple_Bangalore&type=revision&diff=676749674&oldid=676117549.
The reference listing changed to
<li about="#cite_note-6" data-seqid="392" id="cite_note-6"> <span class="cx-segment" data-segmentid="393"> <a class="cx-link" data-linkid="394" href="#cite_ref-6" rel="mw:referencedBy"> <span class="mw-linkback-text">↑ </span> </a> <span class="mw-reference-text" id="mw-reference-text-cite_note-6"><a class="cx-link" data-linkid="395" href="http://www.iskconbangalore.org/deity" id="mweA" rel="mw:ExtLink">ISKCON Temple Bangalore website, Deities page</a>.</span> </span> </li>
But in translation, it was pointing to mw-reference-text-cite_note-5
<span about="#mwt12" class="mw-ref" data-mw="{"name":"ref","body":{"id":"mw-reference-text-cite_note-5"},"attrs":{}}" id="cxcite_ref-5" rel="dc:references" typeof="mw:Extension/ref" contenteditable="false"
data-sourceid="cite_ref-5">
<a href="#cite_note-5" style="counter-reset: mw-Ref 5;">
<span class="mw-reflink-text">[5]</span>
</a>
</span>This caused the following error in parsoid:
extension src id mw-reference-text-cite_note-5 points to non-existent element for: <span about="#mwt12" class="mw-ref" data-mw="{"name":"ref","body":{"id":"mw-reference-text-cite_note-5"},"attrs":{}}" id="cxcite_ref-5" rel="dc:references" typeof="mw:Extension/ref" contenteditable="false" data-sourceid="cite_ref-5">
<a href="#cite_note-5" style="counter-reset: mw-Ref 5;">
<span class="mw-reflink-text">[5]</span>
</a>
</span>I guess we will require a validation about this before publishing.