This might be a bug that's already know but I wanted to check to see if anyone has a workaround.
If you follow a multi-bar percent repeat with a grace note, the result it that the last measure is squashed a bit.
Without the grace note everything is equally spaced.
Here's a small example that illustrates what I am seeing.
\version "2.22.0"
up = \drummode {
\repeat percent 3 { sn8[ sn sn sn] sn[ sn sn sn] }
\grace sn8( sn8)[ sn sn sn] sn[ sn sn sn]
}
\score { << \new DrumStaff << \up >> >> }