Hi, yes I agree. I have contacted them, but no response yet.
It would be good to know what has changed (clearly something has) and as you say, some kind of heads up about these changes.
I am only making an assumption that something has changed, but as you, we haven't made any changes to our platform and we've got multiple accounts being locked with the same error :
326 - To protect our users from spam and other malicious activity, this account is temporarily locked. Please log in to https://twitter.com to unlock your account.
More worrying is that some users have now had this same issue again after already changing their password and if it continues without knowing what the changes are and how to overcome/comply, we're going to start losing users.
All started on or around the date you mentioned and is continuing to happen now.
Will be interesting to see if other users are having the same problem and if we can get any official communication into what has changed.
Please post back if you hear anything and I'll do the same.