I upgraded from 6.40.3 to 6.40.4. On attempting to upgrade the client I am getting this message .
Rolling back to 6.40.3 until further update.

Same problem here, ticket open to the support

This happens also on v6.40 after the tuesday updates from Microsoft.
So I am sure that this is a false positive, but still annoying, because Defender deleted my dude.exe

No other AV product complains, so this is definitely a false positive:
https://www.virustotal.com/#/file/ecd2f ... /detection
https://www.virustotal.com/#/url/d84ac9 ... /detection

same here....

Yup, seeing that on two machines, and reported it when it happened (no response yet).

I found the screen in Defender where I could tell it to ignore anything in the Dude folder, but it was a race to beat Defender itself, which was deleting the Dude exe as fast as I could reinstall it.