https://techcrunch.com/2019/01/17/twitter-bug-revealed-some-android-users-private-tweets/

Twitter accidentally revealed some users’ “protected” (aka, private) tweets, the company disclosed this afternoon. The “Protect your Tweets” setting typically allows people to use Twitter in a non-public fashion. These users get to approve who can follow them and who can view their content. For some Android users over a period of several years, that may not have been the case – their tweets were actually made public as a result  of this bug.

The company says that the issue impacted Twitter for Android users who made certain account changes while the “Protect your Tweets” option was turned on.