Known issue. Grace note synchronisation. Add a spacer in the other staff.
Andrew
upper = \relative c'' {
\clef treble
\key g \major
\time 4/4
\acciaccatura ais8 b8.
}
lower = \relative c {
\clef bass
\key g \major
\time 4/4
\acciaccatura s8 fis8
}
\score {
\new PianoStaff <<
\new Staff { \upper }
\new Staff { \lower }
>>
}
