I played Rappy Slots for 5 hours last night (Ship 1) as the Jackpot maxed out and I didn't notice any improvement of RAPPY PSE Chances/Bursts. As the Jackpot still hasn't been won, can I assume that the boost feature is bugged again?

Even on the JP servers when it maxes out at 500k, it can take weeks for someone to win the jackpot. This is normal behavior.