I have a 2D freeform directional blend tree with the motion fields all setup. It looks exactly how I want it when I play the preview and move the blend parameters manually, but when the game runs, the blend tree doesn’t work as in the preview: the animations operated by the second parameter do not respect the threshold and do not blend at all; instead, they act like separate states, interrupting the other motion fields completely when they are played.
It was just a stupid mistake in the end: I had other two animations outside the blend tree that were using the same transition condition and therefore getting out of the blend tree.