Summary:
Using the solo buttons during a big rock ending after a performance that should qualify for the "Flawless Groove" achievement results in the achievement not being rewarded.
More detail:
I played a song on bass on expert, and hit every note using only upstrums. It should be noted that I did break combo once by strumming when I shouldn't have, but the wording implies only percent hit matters. The song had a big rock ending, so I used the solo buttons to maximize points, then hit the final note with an upstrum. The achievement was not rewarded at the end of the song. I cannot absolutely verify that this is what prevents the achievement, as my next 100% was on a song without a big rock ending for me to try without solo buttons.
Not a huge bug, but figured it was worth documenting.









