Never used soundfonts but may be able to give you some clues and hit the cause by accident.

I assume its similar to using a sampler on a track???
Drum track audio from a midi track? Or is it already recorded to audio?
Partial track recording is off in the switches menu? Then again it's registering and showing notes. I assume you're adding/changing notes on the same track?
Soundfont is an aux effect and the track you are talking about has its fader for the aux on 0 instead of up to hear it and the level meter you're watching is the 'Main' not the Aux.
scoot