Looks great, overall. I can still reproduce step 3 from T234142 with the following error:

Seems related to T233994.

In T233994#5531651, @SUM1 wrote:

Should also mention that this totally breaks the editor, at least it did for me.
Tried to cut a paragraph containing citations, and it failed to cut most of it, and some buttons and functions would not work after this (such as Publish changes or Undo). This was the same behaviour as the vanishing reference, which also vanished when cut (not just "dragged" as the original post suggests). I could no longer Undo or click Publish changes. I'd say this is a very urgent issue to fix.

It's happening again to me today, even in safe mode. Sometimes it looks like the entry finally gets unbold, only for it to become bold again after some time.

Since at least February 12 I cannot reproduce the Error, edit not saved. that I reported. My steps were simply typing "Test https://www.google.com" while logged-out, and now the captcha is indeed shown with no error. Not sure if you're testing some more use cases though.

I would expect it to be consistent with what's shown without any parameters, and it used to work this way when action=raw was paired with usemsgcache=true. The MediaWiki NS currently shows the localized message from the i18n cache if the custom one is deleted. I.e., https://it.wikipedia.org/wiki/MediaWiki:Nextdiff shows "Differenza successiva →".