Does everyone here always reset the amp block in their presets after a major firmware update like this one, or is that only for certain updates?
I always do whenever there have been changes made to the Amp modeling, just to see if any parameter's default values have been altered and not mentioned in the release notes. I then A/B test them against the "old" default values to see if I like the sound of the Amp better with the new settings or not.
For instance, after resetting the USA IIC++ Amp model, I found that the "Power Amp Bias" parameter (located close to the very bottom of the Amp block's Advanced page) default value had changed from a setting of - 0.100 to 0.050. The tone seemed slightly brighter and more open with the new bias value, and slightly warmer and more compressed with the old. It's a subtle difference and I'm not sure which I prefer yet, as I had been playing for at least an hour before doing the comparison and knew not to trust whatever my ears were telling me sounded better.
The point is, the Power Amp Bias parameter's new default value didn't load when the firmware was updated and I wouldn't have known about it if I hadn't reset the Amp model. So it's always a good idea to reset, to be sure you're hearing the latest modeling as intended.
After resetting some of the other USA amp models, I found that their Power Amp Bias default values also changed from - 0.100 to 0.050. I don't know about any of the other Amp models in the Axe-Fx, but I doubt it's just the USA sims that have a new default setting.
I should also mention that, as per usual, the "Preamp Tube Type" parameter (also located towards the bottom of the Amp block's Advanced page) resets to it's default type when the new firmware is loaded. If you have that parameter altered in any of your patches, you'll have to change it back to your preferred tube type and re-save the patch.