Since this update, UdonBehaviours on instantiated objects seem to be inactive for 1.5 seconds rendering any time-sensitive functions on the object broken.
The missiles on my aircraft prefab/worlds are affected by this, because they now take 1.5s to start homing in on their target after firing, which is a very long time for a short-range missile.
If the aircraft's target changes in those 1.5s it takes the new(wrong) target because it can only read the target in Start()
Test world:
Here we have a button to instantiate a cube. The cube is white. The cube has an UdonBehaviour with a Start() function to make change it to a red material.
The instantiated cubes take around 1.5 seconds to turn red.