I played a song on easy bass last night just to get the flawless groove achievement. I achieved 100% but the achievement didn't pop. Does anyone know why? I've read online that you do NOT have to do it on expert. And there's nowhere specified that you have to use only up-strums. I was playing with a friend of mine who was on drums and did not get 100%... could that have possibly affected the results? We were on tour mode, so I don't see how that could have affected it. Can anyone provide any insight? I would like to get these 100% achievements out of the way if I can, but I don't want to keep trying if there is something I am missing. Thanks in advance for your wisdom.