A couple of months ago, a production status site listed Episode IX as filming in 2017. Back then, as many people refused to believe a Star Wars movie would be released in May, the report was brushed off and mocked.
Yesterday they updated their listing to show Episode IX as filming in July:
This is the second time the movie has been listed for a production start this year. Han Solo is currently filming, and likely will be done by the time July rolls around. That movie is set for a May 24, 2018 release.
If Episode IX is really being targeted for a May 23, 2019 release, it’s definitely believable that they’ll begin production of it this year after they finish with Han Solo.