This is a problem with the Octatrack.
Like many synths, the Hydrasynth uses the second part only of the MIDI Bank Select message. Unfortunately, the OT’s Bank setting sends only the first part of the Bank Select message.
To change bank on the Hydrasynth from the OT, you need to send MIDI CC message 32 (with a value in the range from 0 to 4) immediately before sending the Program Change message.