I’ve also experienced latency when switching programs. The spillover does help mask it, but it is not instantaneous and I’ve had to switch ahead of the part when when changing programs. It’s really obvious when you click on a button and it doesn’t engage until your foot is almost back on the floor.
Digital pedals will always have some latency for loading the next program. (Note that you won’t have the same issue when switching off and on, either with digital or analog pedals)
The H9 also lagged when switching between algorithms (the time dependent on the algorithm) and would drop out between algorithms.
In short, I believe that this is just how the pedal is.