Hi, I believe I am having the same issue, I’ve only been able to use the app at home for now so not pushing it past a low level of volume.
I noticed this when using headphones, and I recommend you do the same, despite having gain as low as possible, no effects activated and trying all three amp types (vintage flat modern) I am getting an overdriven sound even at low volume, and adding gain or even just raising master volume makes it very noticeable, for reference, I am playing a jazz bass with flats, so not what I was expecting.
If you could confirm this also occurs for you with headphones, I think we might have the same problem, not a speaker issue but perhaps with the preamp.
I tried that and came to the same conclusion. The pad doesn't clean up the headroom, it just makes the overdriven sound -10 dB quieter. I'm moving on from this, I hope you find a suitable solution that works for you.