On June 2, 2019, Google did something it had never done before: it pre-announced a core update. @searchliaison tweeted "Tomorrow, we are releasing a broad core algorithm update, as we do several times per year. It is called the June 2019 Core Update." Danny Sullivan said there was nothing exceptionally big about this particular update; Google simply wanted to be more communicative so site owners would not be left "scratching their heads after-the-fact".
The next day Google confirmed the launch: "The June 2019 Core Update is now live and rolling out to our various data centers over the coming days." No completion date was announced. The same week Google also launched a separate site diversity change, which aims to show no more than two listings from the same domain in top results; Google stated explicitly that "the site diversity launch is separate from the June 2019 Core Update that began this week."
As a broad core update there was nothing specific to fix. If your site moved in early June 2019, audit it against Google's core updates documentation and its self-assessment guidance, and see our recovery guide for the sequence.