CoPilot has suddenly stopped working in Word?

I agree this is most likely a backend issue but ot from the client side or local.

Would suggest handle as same as the M365 problem which is to raise a ticket with Microsoft support.

https://learn.microsoft.com/en-sg/answers/questions/5914822/how-to-fix-oops-something-happened-can-you-try-aga

https://learn.microsoft.com/en-us/answers/questions/5920939/copilot-isnt-working-inside-a-word-document

Since the failure happens in Word desktop and web on two Windows versions, while Copilot works in other Microsoft 365 apps, it does not look like one damaged Word installation. It is more likely a Word-specific service, document, account, or tenant condition, so record the time and test with a new blank document stored in OneDrive. That distinguishes a document-specific problem from the Word service path. Verify the affected account is the licensed account in Word, sign out and back in once, and install the latest Office updates. Check the Microsoft 365 admin center’s service health for Word or Copilot advisories. If the blank document fails in both clients and service health is clear, collect the Word version, browser version, tenant, approximate timestamps, and any request ID shown with the error, then reopen the Microsoft support case. No client-side repair can prove a server-side Word Copilot fault is resolved.

Yeah, I've seen this pattern before and honestly the "backend issue" line from support chat is usually the right instinct, just given too early, before anyone's actually confirmed it. The part that stands out to me is that it's happening in both the desktop app and the web version, on two different Windows builds. That combo basically rules out a local install or profile problem those two don't share any cache or code path, so if it were something broken on your PC, you'd expect at least one of them to still work.

A couple of things I'd check before just waiting it out: first, if this is a work account, have your admin look at Service Health in the M365 admin center support agents will say "backend issue" even when nothing's officially logged yet, so it's worth confirming there's actually an incident tied to it. Second, try a brand new blank document saved to OneDrive, just to rule out one specific file being the culprit. And if you're on a managed tenant, it's worth asking IT to double check Word specifically hasn't been scoped differently than Excel/Outlook in the Copilot settings that's a surprisingly common cause of "everything works except this one app."

If it's still broken after that, don't bother repeating yourself to support chat use Help > Feedback > "Something didn't work" right when the error happens. That attaches a correlation ID, and that's the one thing that actually gets a real fix moving instead of another canned response.