I have just had the same issue, almost. I was checking a Word doc (Word 365) in Grammarly when suddenly it was as if someone was holding down the delete key. I could do nothing as the words were literally eaten by the cursor, line after line. I have checked
the article in the link you provided but, when I started Word, there was no Document Recovery window showing and 'recent unsaved documents' didn't show any documents from today; yesterday's were there, but not the 1,300 words I had just typed.
For added info: Document auto save was on for every five minutes, and I had been working on the doc for at least half an hour so it should have been AutoSaved.
The only way to stop the words from being eaten was to Ctrl + Alt + Del and end in task manager.
Both Grammarly and Office/Word are legit, paid for subscriptions and up to date.
My keyboard is fairly new and no keys are sticking. I've always used this make of keyboard with this PC (Windows 10, 64 bit) and had no issues.
I can't find anything in a search for .tmp
I don't know what can be done except to answer the question: where else might I find unsaved files if/when Document Recovery fails to show up after a crash.
The other answer, of course, is to save the work manually every few seconds, but then that's what Auto Save is meant to do and in this case, it failed. Perhaps it's a problem with the Grammarly/Word relationship.
Totally frustrating!