Following the lukewarm response to Fantastic Beasts: The Crimes of Grindelwald, it was announced in early 2019 that Fantastic Beasts 3 production would be delayed from the summer of that year to late fall.
It was stated at the time that pre-production just needed more time as the plans for the third film were quite extensive.
This is just the latest delay in a line of slowdowns and stalls that go back two years.
However, things ended up taking even longer than that as, when the fall of 2019 rolled around, it was announced that filming would actually start in the spring of 2020.