Honestly I agree more with
@Shiroyru and
@Fujishiro 's takes. Its CD infighting caused by the Revolutionaries destroying their supplies.
Shamrock needing to go back made sense since, at that point, his father was just promoted. Assuming he then went from Captain to Commander of the HKs, he may have been given to authority to calm down or even slaughter the troublemakers. Also he might be able to stop the RA sabotages.
The reason i doubt the RA assault yet is you'd assume Oda wasnt repeating their recent Reverie attack and when they do actually attack he'd show it.
And based on this, it does seem like Laffite has some role to play there: