I am not sure if it's a limitation of cx-testing environment.
Steps to reproduce:
1. In cx-testing click on New translation: select English to Russian translation. The name of the article to translate is 'Platonic solid'
2. Do some cursory translation and publish it as Personal Draft. The Following error will be displayed.
When attempting to publish it as New page, the same error is displayed.
When attempting to publish [[ http://cx-testing.wmflabs.org/index.php?title=Special:ContentTranslation&page=%D0%9F%D1%80%D0%B0%D0%B2%D0%B8%D0%BB%D1%8C%D0%BD%D1%8B%D0%B9+%D0%BC%D0%BD%D0%BE%D0%B3%D0%BE%D0%B3%D1%80%D0%B0%D0%BD%D0%BD%D0%B8%D0%BA&from=ru&to=en&targettitle=User%3AET1%2F%D0%9F%D0%BB%D0%B0%D1%82%D0%BE%D0%BD%D0%BE%D0%B2%D1%8B+%D1%82%D0%B5%D0%BB%D0%B0 | Правильный многогранник ]] to User:ET1/Платоновы тела (my test user space) I got
```
An error occurred while publishing the translation. Please try to publish the page again. Error: Error converting HTML to wikitext: docserver-http-error: (curl error: 28) Timeout was reached
```
The stack trace:
```
mw.Api error: docserver {error: {…}}
[CX] Error while publishing: docserver
{sourceLanguage: "ru", targetLanguage: "en", sourceTitle: "Правильный многогранник", sourceRevision: "87530953", targetTitle: "User:ET1/Платоновы тела", …}
error: {error: {…}}
sourceLanguage: "ru"
sourceRevision: "87530953"
sourceTitle: "Правильный многогранник"
targetLanguage: "en"
targetTitle: "User:ET1/Платоновы тела"
__proto__: Object
```
{F9633147}
//Note: //I was able to do the similar test on Jul 24: User:ET1/Test on July 24
//Note:// There was a report by a user https://www.mediawiki.org/wiki/Topic:Tyijou0rmux5218z. I repeated the above steps on the article reported: Chinese Garden of Friendship (English->espanol).
{F9711006}