Ok, so I noticed that the MIDI note extends past the MIDI block. When I shortened the MIDI note so that it was exactly as long as the MIDI block, the next time the MIDI instrument would be retriggered (at bar 11) it actually was retriggered as expected.
Why would NUENDO continue to play a MIDI note when it extends past the end of a MIDI block? As a user, if I cut off a MIDI block, I expect any MIDI notes to stop playing right where the MIDI block was cut off.