Cubase Not Triggering All Legato Notes Of External Synth

If I draw a series of legato notes in a MIDI track then output that to an external synth (via USB or MIDI Out of MIDI keyboard) some of the notes are triggered, where as some random notes are not triggered (the random notes change with every cycle).

If I shorten the notes by 10 ticks all the notes are triggered as expected.

Does anybody know what the problem is?

I’ve tried 2 different synths and different MIDI cables and the result is the same.