Oh dear.

We had just ruled out VisualEditor itself being an issue (was most likely something deep in MessageCache or ParserOutput) when the bug mysteriously disappeared. :/

It's still broken on dewiki Beta Cluster.

Is it confirmed that this is not caused be presence (or lack of presence) of mediawiki.jqueryMsg? Or is this message generated on the server side?

T136124: VisualEditorDataModule triggers "Sessions are disabled for this entry point" might or might not be related.

Now happening in production on mediawiki.org as well.

And while it fixed itself on enwiki Beta Labs earlier, it's now broken again on enwiki Beta Labs for me.

In T136109#2325334, @Nikerabbit wrote:

Is it confirmed that this is not caused be presence (or lack of presence) of mediawiki.jqueryMsg? Or is this message generated on the server side?

The parsing of these is done on the server side from an RL module.

In T136109#2324880, @Jdforrester-WMF wrote:

It's still broken on dewiki Beta Cluster.

In T136109#2327139, @Krinkle wrote:

Now happening in production on mediawiki.org as well.

In T136109#2327139, @Krinkle wrote:

And while it fixed itself on enwiki Beta Labs earlier, it's now broken again on enwiki Beta Labs for me.

These all WFM

Cant reproduce it anywhere either.

I'm OK with declaring this a Beta Cluster infrastructure temporary bug and closing for now…

This was definitely in production as shown above. I believe this may've been a side-effect of T136124.

Oh, hmm. Yeah, that looks plausible.