If you land sneak attack on your turn, and afterwards land an Attack of Opportunity, you can apply Sneak Attack twice within the same round.
Unfortunately, if you do apply Sneak attack to an Attack of Opportunity, you won't have it available for the Rogue's next turn.
They could make it so Sneak attack refreshes both at the beginning, and end of the Rogue's turn. That way both the Rogue's turn and their reaction will have access to the Sneak Attack damage.
Currently, Sneak Attack only refreshes at the End of the Rogue's turn, which is where the issue comes from.
