This might be a train blocker for {T392177} because I can reproduce the following issue on 1.45.0-wmf.7 (e.g. mediawiki.org) but not on 1.45.0-wmf.6 (e.g. dewiki).
Steps to reproduce:
* Make sure you have the preference enabled to "use the wikitext mode inside the visual editor".
* Start editing any article in VisualEditor.
* Make at least one change, e.g. add a character.
* Switch to source editing with one of the two methods available in the toolbar(s) at the top.
* A popup appears: "Invalid response from server."
* When I click "Try again" the code apparently does **not** try to do the same again but does a different API request in the background. As a result the edit I just did gets lost.
When I monitor the network traffic I see:
```lang=json
{
"warnings": [
{
"code": "unrecognizedparams",
"html": "Unrecognized parameter: editingStatsId.",
"module": "main"
}
],
"visualeditoredit": {
"result": "success",
"content": "…"
}
}
```
This might or might not be related. The code that appends this parameter is in #WikimediaEvents, see https://codesearch.wmcloud.org/search/?q=editingStatsId.
We have also seen the wikitext disappear completely but are not able to reproduce it.