A quick update: Looks like when we QT a past tweet, it shows up properly in the mobile app (left), but say this "this post is unavailable" in the browser version (right).
Still investigating and trying to reach out to Twitter support. Rest assured that no past tweet has been deleted as shown in the left image.
@Epricity@antiqueshows@marginfi Hey there! You’ll need to connect your Mem account to Twitter before you can start saving tweets to Mem. Head to https://t.co/gi553Krou2 to sign up for an account and set up the Twitter flow.