Johnny was spotted in Lacock, Wiltshire, England for Fantastic Beasts 3.
Fantastic Beasts 3 is scheduled for release in November 2020, continuing the pattern of the first film (November 2016) and its sequel (November 2018) but nothing has been confirmed yet. There are two more sequels to come, which means 5 Fantastic Beasts movies in total. We don’t know yet whether Johnny will appear as Grindelwald in the fourth and fifth movie though.
As the headline says, I marked this post as a rumor since it has NOT been confirmed whether Johnny’s stay in Lacock is connected to the start of production of Fantastic Beasts 3 or whether he was really seen at all. The news website reporting his appearances is Wiltshire Times.