When the tempo is slow the acciaccatura made with a grace note is too long.
In some extreme cases, even 1/64 in a hidden staff is too slow.
You might try something like this:!NoteWorthyComposerClip(2.751,Single)
|MPC|Controller:tempo|Style:Absolute|TimeRes:Quarter|SweepRes:1|Pt1:0,10|Pos:12
|Note|Dur:8th,Grace,Slur|Pos:4
|Note|Dur:4th|Pos:3
|MPC|Controller:tempo|Style:Absolute|TimeRes:Thirtysecond|SweepRes:1|Pt1:0,120|Pt2:1,10|Pos:9
|Note|Dur:8th,Grace,Slur|Pos:4
|Note|Dur:4th|Pos:3
!NoteWorthyComposerClip-End