I've been facing this issue for the last 4-5 days. It's super annoying.

However, I have found a few work arounds to cancel existing bookings, make new bookings and apply SNAs.

You can still access a reservation if you can find your confirmation number in your e-mail. On the My Trips page, click "don't see your reservation? search by confirmation number" and type in the details. From there, you should be able to apply suite nights or cancel the reservation entirely.

To make new bookings, I've found that I can do this by making a booking without being logged into my Marriott.com account. Make the reservation as a guest and check out. After you've made the booking and receive the confirmation e-mail, search for the reservation per my instruction above and you can add your Bonvoy number manually under guest info.