CoPilot has suddenly stopped working in Word?

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.