Yeah, that's just the way it goes.
For example, I seem to be stuck on "Detroit Rock City" for expert vocals, and that's an AWFUL song. You miss a phrase and you lose like, half your meter.
"Dead on Arrival" expert drums, stuck for three weeks, awful song.
"Green Grass and High Tides" expert guitar, stuck for a month. Bad song, not awful, but sooo loong. Finally beat that bitch. The trick is to just play the first three notes of those 4 note repeating patterns in Solo 2 J-M.
I'm stuck on "Don't Fear the Reaper" now for expert drums and it's not that song is bad, it's just that it's LOOOONG.