BMO service desk down or account closed?

From the description, this looks more like a risk-control trigger than a full account closure. Since the issue came up right after you completed DD, don't rush to log in repeatedly or move your balance. Take screenshots to preserve the page state, then call customer service directly to clarify your account status and whether you need to submit any additional documents.

If you're in the U.S., asking at the counter in person is fastest—but first make sure you have your card and ID with you, and don't rely on just a single statement over the phone.