The community has found a bunch of game-breaking bugs related to the buildable structures update, most of them related to saving the game. This is what's still blocking me from releasing this big update to the main, public branch.
I have just patched all known issues up, released a new build to the test branch, but the official release of this update still has to be postponed a couple of days. Still working on it, and it's gonna finally come out, really soon.
Changed depots in new-features-testing-build branch