Ardour + Virus B sync issues

I seem to have trouble getting Ardour to start playing notes from my Virus B at the correct time. (I have a similar issue with the Blofeld, but nudging the MIDI region a little earlier consistently solves this problem. The same strategy does not work consistently with the Virus B.)

What I have tried so far is patching Ardour’s MMC out to the Virus B’s MIDI in via my MIDI interface. This seems to help somewhat, but it’s still not consistent.

Has anyone had a similar issue with any instrument? If so, how did you solve it?

No information on the version of Ardour, the platform, the MIDI bridging in place …