When you start playback at a point that's in the middle of a held chord, Logic will only chase some of the notes. At the point where the chord should end, notes that Logic didn't play back originally may sound very briefly.
This issue occurs when the notes in a held chord are staggered, and you start playback after the first note (or notes) occur, but before the later note (or notes) begin. For example, if you start playback at the point depicted below, the notes will not chase properly:
However, if you move the playhead so that playback starts after the later notes in the chord begin (as shown below), then the notes in the entire chord will be chased as expected.
This document will be updated as more information becomes available.