D0 and F#0 play no sound

Using Halion Sonic SE, when I play the notes D0 and F#0, no sound is played.
The MIDI activity indicator jumps when I press the key on my controller and I have also tried using the computer keyboard (ALT-K) and the same thing happens.
I tested multiple patches in Halion Sonic SE and Halion One as well.
There are no keyswitches assigned to these keys in the patches I have tried (at least none visible with the brown shading).
The notes play if I click directly on the key in the piano roll in Halion Sonic SE.
So it seems that the controller (and computer keyboard) are sending data but with those two notes, they trigger no sound.
I am sure there is some logical reason for this (reserved for keyswitches or sysex?) and I am really curious why it happens.

Can anyone confirm for me that this is not just on my end please?