Hello! Forgive me if this has been solved before I am new to this forum. I seem to have this issue a lot! I will have a flute (or any instrument it never stays consistent) that is sustained for 12 counts. After about three counts the midi drops out 
! Is there any solution to this, please let me know if I need to provide more information, thank you!
It would be best if you have a demo project that exhibits that problem and then attach here (after zipping it up).
Does it happen only with complex scores where many instruments are playing at the same time or also with smaller arrangements?
If it only happens on with large scores, have you checked the Options tab in the HALion Sonic editor window? You might play around with the setting for maximum amount of voices and multi processing.