In my pillaging I find that the "recent uprising" modifier only seems to apply to provinces at random - I often go 3+ uprisings before I see the modifier applied to a province I'm pillaging. Is this a bug or am I missing some bit of info?
Recent uprising is only applied to additional rebellions of an active one.
So you might have a sunni uprising, no recent uprising is applied. When additional forces join that uprising, the modifier is then applied to the county they spawn in.