I have come across a bug where in some instruments there are notes that don’t sound under certain circumstances. The affected instruments I’ve found are “Real Pick Rock Bass”, “Real Fingered Modern Bass” and “Real Vintage Bass”. All of these have almost the same articulation scripts which involve legato detection.
The way you can reproduce the bug is to have a number of adjacent notes like in the attached image, and play them using any of the mentioned instruments. In some cases there will be skipped notes. The weird thing is that the bug happens much more when ASIO buffer size is bigger. Try 512 samples or 1024 and see. Of course this sequence is a way to force the bug but it can happen in a normal sequence, as it does to me.
My programming experience suggest that this bug may be produced by incorrect MIDI event alignment or execution within the same ASIO frame (had that bug in a sound driver I programmed recently), but of course I can’t know in Halion. Hope it helps a bit. Also, the bug happens when freezing the instrument (which suggest that it’s frozen using the same frame size than in real time).