I remember there was a time after Musk took over that they changed the API so that only logged in users could access it. That broke all of their widgets on third-party websites, which Twitter neglected to update. The widgets phoned home every few seconds, which DDOSed themselves with their own widgets.
I dunno about going down entirely, but bits and pieces (like SMS verification) definitely broke while they were undoing work and cutting "expenses" (like office leases)