After the latest patch, sea encounters now often require a battle in order to get the full reward. I have just sailed to a wreck, which gave me the option to Explore the Island or Wait (for an inferior reward). I chose the former and the game zoomed in to an enemy army on an island, after which nothing further happened. I tried to attack that army, but the game did not allow it.
Thinking that perhaps I didn't have enough movement points, I reloaded my saved game, sailed close to the wreck, then waited until the next turn to sail onto it. Exactly the same thing happened: no battle, and no way to initiate one.
My army is in the normal stance (No Stance), not Double Speed or any stance which would prevent attack.
I'm playing the Mortal Empires campaign as Bretonnia.