Additional Update–Saturday, August 11: The form email from Twitter instructed me to reply to if the issues continued after a few hours. I sent a reply this morning.
I can log in but can do almost nothing other than view content and unfollow accounts. Twitter won’t allow me to tweet, like or retweet, follow anyone new, add to lists, or send direct messages. These activities are blocked with alerts.
What’s new is that unlike a couple of days ago, I was able to submit a contact form to Twitter from its Help Center.
Twitter responded with a generic response asserting that my account “may be compromised by a user or a service not associated with Twitter.” The email contained simple instructions, which I’ve followed. I’ve also checked again for any signs of suspicious activity or unauthorized connections within my account. For the record, I’ve found none.
Again, I’m waiting to see what happens next.