Does it sound OK at 48k/44.1k? It's possible that the algorithm needs changes to work at higher rates, since it originates in the H9, which has a fixed sample rate. We will look into this.
This is not normal. The four FX chains should be completely independent, so what's running on the first three should not affect the fourth. What is the routing to/from the fourth FX chain? What happens if you bypass the fourth FX chain, or use Direct IO to bypass the DSP completely?