According to the distribution website the release date for the Down AT-ST Battlefield Expansion is now June 27th. Previously it was May 30th.
It looks like May 2019 will be the first month since Star Wars Legion incarnation that there will not see any new releases.
Fantasy Flight Games has had a pretty consistent release schedule so far. It is unclear at this time why new releases have seemed to be delayed.
The speculated release of the Bossk and Sabine Operative Expansions were previous late May, are now speculated to release early June.
Check back for updates as they come available.