Google+ is closing the consumer functionality of Google+ due to lack of adoption and an API bug that leaked the personal information of up to 500,000 Google+ accounts. Google+ will be closed over a 10 month period, while Google transitions the product to be used internally by the Enterprise. The Wall Street Journal reported that an internal committee at Google decided not to disclose the bug even though they were not 100% sure that it was not abused. The leak occurred between 2015 and March 2018, which was when Google discovered and fixed the bug.
Source: https://www.bleepingcomputer.com/news/security/google-shutting-down-after-bug-leaks-info-of-500k-accounts/