For those commenting on a difference in perceived treble and/or presence on the new beta 12, I may have found a possible cause for this.
Each time the beta firmware update is performed (from beta 11 to beta 12 for example), the Power Amp Grid Bias parameter is re-set to the default value for that particular amp model, even if you had previously updated and saved your patches in beta 11 with modifications to the Power Amp Grid Bias to a value different than the default value.
If your patches were originally created with a relatively hot power tube grid bias (0.6 to 0.7 for fixed bias amp models), they will rest to a default grid bias (0.45 to 0.5 in some models) when updating to beta 12. The drop in grid bias simulates a colder bias in the power amp tubes. Patches originally created in firmware 15 and earlier might have had a "hotter" default value for the power amp grid bias also (?), although this parameter has been completely reworked for firmware 16.
This drop in the bias value when the grid bias is re-set to the default value when updating to beta 12 could cause a reduction in overall volume on your patch, which can seem like having less treble, less presence, etc. when you hear it.
Each time the beta version has been updated, I've gone in and manually re-adjusted all my presets with my preferred power amp grid bias for fixed bias amp models. Hotter power amp grid bias is typically in the 0.6 to 0.7 range for fixed bias amps (the majority of amp models), which I personally prefer for my patches.
For cathode biased amp models (5E3 Deluxe, AC-30, etc.) the default power amp grid bias is 1.00, which authentically models a cathode biased amp. Presets with cathode biased amps would not need to be tweaked in that case when you update the firmware.
The power amp grid bias parameter is in the "Advanced" tab, under the Power Amp section - "Grid Bias"
Personally, I find this grid bias parameter in the Cygnus firmware is very authentic, as it now behaves exactly as how I would bias the power amp tubes in a real tube amp.
I hope this helps.