Created a note to form the basis of a baseline and each note was as long as 1 bar. I copied and pasted it along and changed a few pitches.
On playback the 5th or 6th bar along doesn't play the note at all!
Solution quoted:
It has to do with the notes being abutted exactly up against each other. When the note-off time is equal to the note-on time and the pitch is the same, apparently the DLS SoundFont plug-in gets confused and occasionially turns off the just-turned-on notes. The solution is to subtract 1 from all the note durations. I will look into this further to make sure Metro is sending the note ons/offs exactly as they should be sent to the plug-in.
Solution works!
Thanks Jerm.