Hi!
In your first example, had your troops assault orders and actually engaged the units inside the fort?
If they just landed on the region and there was no combat i think it's normal there was no bombarding in support.
As the Grandpre units did not have guns to fire on the ship, no bombardment was triggered because of this either.
In any case, now that i think of it...

what Lodi says looks pretty reasonable: that ships cannot bombard structures without port, as they can be way inland.
In this example, fort Granpre could be several days of march inland from the coast, and 100 miles out of ships range. Regions are very big.
A structure with a port is coastal and could be fired upon from the adjacent sea region.
What i have no idea is how this woudl work on regions without structure

Is the battle inland or on the coast
Regards!