I have recently run into this the issue where synplant is no longer responding to midi input. It worked in previous projects but most recently when I open a new set the software seems to not be producing any output.

Synplant not responding to MIDI input is almost always the MIDI input channel not set correctly. Please double check the Synplant MIDI Settings.

https://soniccharge.com/forum/topic/776-synplant-produces-no-sound