For me filter 2 is behaving the same way, and that is after it was serviced by DSI. When I received it (2nd hand) the lowest I could get the resonance peak to was 300Hz. Users on another forum showed me spectrum analyzer pics of their filter which went down to 28Hz (3,5 octaves difference!!) So I sent it in and after serviving I'm now able to get it to 100Hz (still 2 octaves..). It's better than before but sadly, this strips the synth of many many capabilities for me, the filters are the most delicate modules in a synth after all...
The Dave Smith Instruments Pro 2 Analogue Synthesizer