Users deleting many Tweets in a row from their profile.
Users who run a mass-deletion program like TwitWipe, TweetEraser, or DeleteMyTweets.com on their profile.
We do not advise using mass-deletion programs. If you deleted many Tweets because you wanted a fresh start on Twitter, click here for instructions on how to start over afresh.
Tweets more than a week old may fail to display in timelines or search because of indexing capacity restrictions. Old Tweets are never lost, but cannot always be displayed.
I'm missing direct messages:
Direct messages can be deleted by either the sender or the recipient at any time and will be removed at that point from both users' message histories. If your DM is missing, it's likely that the person you were communicating with deleted the message. Learn more.
The number of Tweets I see on my profile looks wrong:
If the Tweet count displayed on your profile page does not match the number of Tweets displayed on that page, this can be caused by users deleting many Tweets in a row from their profile OR by users who run a mass-deletion program like TwitWipe, TweetEraser, or DeleteMyTweets.com on their profile.
Again, we do not advise using mass-deletion applications. If you're looking to get a fresh start on Twitter, click here for instructions on how to do so.
We are aware of the issue with the deletion of multiple Tweets and are working to restore Tweet counts to users affected by this issue. Follow @Support for updates.
Tweets don't appear where I expect them to:
We often hear from users who are confused about where their Tweets appear. Mentions and @replies, for example, only appear on your own home timeline and in the Mentions tab of the user to whom you replied. @replies do sometimes appear when the original Tweet is expanded, but due to capacity restrictions not all @replies will appear in an expanded Tweet.