The following input breaks when translated using cxserver:
Produced on https://dev.translatewiki.net/w/i.php?title=Special:ContentTranslation&page=Vantaa&from=en&to=es&targettitle=Vantaa&version=2 (first section after infobox).
<section id="cxTargetSection1" data-mw-cx-source="undefined"><p id="mwBQ"><span data-segmentid="218" class="cx-segment"><b id="mwBg">Vantaa</b> (<small about="#mwt7" data-mw="{"parts":[{"template":{"target":{"wt":"IPA-fi","href":"./Template:IPA-fi"},"params":{"1":{"wt":"ˈʋɑntɑː"}},"i":0}}]}" id="mwBw" typeof="mw:Transclusion" data-ve-no-generated-contents="true">Finnish pronunciation:<span typeof="mw:Entity"> </span></small><span about="#mwt7" class="IPA" id="mwCA" title="Representation in the International Phonetic Alphabet (IPA)" data-ve-ignore="true"><a class="cx-link" data-linkid="219" href="./Help:IPA/Estonian_and_Finnish" rel="mw:WikiLink" title="Help:IPA/Estonian and Finnish">[ˈʋɑntɑː]</a></span>; <a about="#mwt8" class="cx-link" data-linkid="220" data-mw="{"parts":[{"template":{"target":{"wt":"lang-sv","href":"./Template:Lang-sv"},"params":{"1":{"wt":"Vanda"}},"i":0}}]}" href="./Swedish_language" id="mwCQ" rel="mw:WikiLink" title="Swedish language" typeof="mw:Transclusion" data-ve-no-generated-contents="true">Swedish</a><span about="#mwt8" data-ve-ignore="true">: </span><i about="#mwt8" lang="sv" data-ve-ignore="true">Vanda</i><link about="#mwt8" href="./Category:Articles_containing_Swedish-language_text" id="mwCg" rel="mw:PageProp/Category" data-ve-ignore="true">) is a city and <a href="./Municipalities_of_Finland" rel="mw:WikiLink" data-linkid="221" class="cx-link" id="mwCw" title="Municipalities of Finland">municipality</a> in <a href="./Finland" rel="mw:WikiLink" data-linkid="222" class="cx-link" id="mwDA" title="Finland">Finland</a>. </span><span data-segmentid="223" class="cx-segment">It is part of the inner core of the <a href="./Greater_Helsinki" rel="mw:WikiLink" data-linkid="224" class="cx-link" id="mwDQ" title="Greater Helsinki">Finnish Capital Region</a> along with <a href="./Helsinki" rel="mw:WikiLink" data-linkid="225" class="cx-link" id="mwDg" title="Helsinki">Helsinki</a>, <a href="./Espoo" rel="mw:WikiLink" data-linkid="226" class="cx-link" id="mwDw" title="Espoo">Espoo</a>, and <a href="./Kauniainen" rel="mw:WikiLink" data-linkid="227" class="cx-link" id="mwEA" title="Kauniainen">Kauniainen</a>. </span><span data-segmentid="228" class="cx-segment">With a population of <span about="#mwt181" data-mw="{"parts":[{"template":{"target":{"wt":"formatnum: {{Infobox Finnish Municipality/population count|Vantaa}}","function":"formatnum"},"params":{},"i":0}}]}" id="mwEQ" typeof="mw:Transclusion" data-ve-no-generated-contents="true">221,821</span> (<span about="#mwt10" data-mw="{"parts":[{"template":{"target":{"wt":"#time: j F Y","function":"time"},"params":{"1":{"wt":"{{Infobox Finnish Municipality/population count|sourcedate}}"}},"i":0}}]}" id="mwEg" typeof="mw:Transclusion" data-ve-no-generated-contents="true">31 August 2017</span><sup typeof="mw:Extension/ref" data-ve-ignore="true" data-mw="{"name":"ref","attrs":{"name":"population_count"},"body":{"html":""}}" class="mw-ref" about="#mwt12" id="cite_ref-population_count_3-1" rel="dc:references"><a href="./Vantaa#cite_note-population_count-3" style="counter-reset: mw-Ref 1;"><span class="mw-reflink-text">[1]</span></a></sup>), Vantaa is the fourth most populated city of Finland.</span></p>
</section>As a side effect, this causes
jQuery.Deferred exception: model.getSectionNumber is not a function TypeError: model.getSectionNumber is not a function
at VeInitMwCXTarget.<anonymous> (https://dev.translatewiki.net/w/extensions/ContentTranslation/modules/ve-cx/init/ve.init.mw.CXTarget.js?3496c:678:46)
at fire (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3268:31)
at Object.fireWith [as rejectWith] (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3398:7)
at process (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3622:22)
at Object.<anonymous> (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3632:9)
at mightThrow (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3534:29)
at process (https://dev.translatewiki.net/w/resources/lib/jquery/jquery.js?6a07d:3602:12) undefinedThis is because model is VeDmCXPlaceholderNode and it is that because translation failed, tries to fallback to the source text, but that one fails too, and placeholder is not replaced with new content.
Related ticket: T205616: CX2: Section alignment broken when translating "Fleming: The Man Who Would Be Bond" from Hebrew