For General MIDI compatibility, the default sound font instrument assignments are bank 0, program 0 ("Acoustic Grand Piano") for channels 0–8 and 10–15, and bank 128, program 0 ("Default Drum Set") for channel 9.
Apparently, your sound font does not have the latter.
This does not matter if your MIDI file does not assume General MIDI compatible instruments and does not try to play drum sounds on channel 9.