Going Solo achievement issues?

So I never bothered getting the Going Solo achievement in Rock Band before, but I got the itch to do it this week so I went through all of my songs to get it. When I started, my achievement in the tracker was at 50%, so I figured I'd end up replaying some songs that I've already done in the past, but showed no scores due to leaderboard wipes, but oh well. It happens.

Played a good dozen or so songs, achievement tracker never budged. Played the the tracker displaying on a few more songs, nothing. I honestly expected the tracking was fucked up and didn't think about it.

Today, I played up the last songs I have from RB4 on disc and my tracker is still at 50% and no achievement.

is the achievement bugged? Did the newest update mess it up? I REALLY don't want to have to play all the on disc RB4 songs with solos one more time since they all have scores now...