I ran across your post under the BFD3 Topic in the Cubase Forum and deleted my post as there was no need for the troubleshooting I posted here.
There are quite a few users in this Forum using Cubase with BFD3, so hopefully some will chime in…
EDIT:
if it’s of any help…personally when using drum modules etc as controllers I get it working well in the Standalone first and that helps eliminate some trouble shooting when moving to Vst/DAW.
Connect the DTX MULTI 12…load the DTX-MULTI 12 Key/Map and check…if the mapping seems out of wack check the Octave range…Tools > Preferences > MIDI.
I setup mainly Alesis Modules and the Octave needs to be set at -2 for the maps to line up properly
if you didn’t use the Setup Wizard to select the Host/DAW.
There is also an extension for using the DTX-MULTI 12 as a controller in Cubase ,don’t know if you already have it setup that way or may or may not be interested in it.
"DTX-MULTI 12 Extension is software which lets you operate the Cubase functions from the DTX-MULTI 12 as a remote controller. For example. You can operate the Cubase transport, turn its metronome on or off, and control various other functions from the instrument’s front panel.
For more details, please refer the installation Guide which will be downloaded with program file."