I'll just add that for the past several weeks, all of Sonder's own support channels have been completely unresponsive to me (phone/chat/e-mail). Definitely book through Marriott, at least their customer support is still reachable.

I'm hoping I have no check-in issues that require contacting Sonder for a stay starting this week; I've been so frustrated by the experience that I've cancelled two future Sonder stays until I feel confident that Marriott has fully taken over all customer servicing aspects.