I'm a new HELIX user. Reading the forums I saw where some were commenting on the volume pedal being inconsistent when switching presets. Turns out a parameter setting can fix this. In the Global settings for Footswitches, change the expression pedal setting from preset to global. Thanks to YouTuber Ben Vesco for the tip.
DaveJ
ADDENDUM: Just want to add that where you find these parameters will depend on what firmware version you have. Right now my new unit from Sweetwater is on 2.30.0. For that version Exp 2 is volume. It may be different on 2.92.0 or other versions. Also, I found that it will matter how the preset is configured. I found several default presets that DO NOT have a volume pedal. You can rock that pedal all you want. It won't make a difference.
DaveJ