Dear all,
I am Japanese and so sorry my humble English.
I am facing the same (maybe) vol problem with 2.90.
Helix-Floor, tested Main Vol only (phone vol not been tested), Footswitch=Preset mode, 1/4 out, FRFR.
(1) Trial-01 (Helix floor is turned off)
Set Vol=0 (around 7 oclock), turn it on and boot, helix wake up at preset 10C (for e.g.)
but nothing can be heard, Level meter is working.
sometimes preset change does not even work, like hang-up. You cannot to anything.
(2) Trial-02 (Helix floor is turned off)
Set Vol=not zero e.g., 3 (around 10 oclock), turn it on and boot, you can hear the sound of helix preset 10C.
Tweaking vol, but it does not change, sound level you hear stays te same. Sometimes you cannot do preset change, tuner mode, etc.
(3) Trial-03 (Helix floor is turned off)
Set Vol=not zero e.g., 3 (around 10 oclock), turn it on and boot, you can hear the sound of helix preset 10C.
NEVER TOUCH VOL KNOB.
Preset change (e.g., 10C->10B->10D whatever), then into Stomp mode, turn on-off some of your effect chain,
then into tuner mode (tuner mode = sound-muted), then get out of tuner mode to come back to previous mode (Stomp or Preset).
Vol Ctrl is working :-) as normal (hopefully)
(4) Trial-04 (Helix floor is turned off)
Set Vol=not zero e.g., 3 (around 10 oclock), turn it on and boot, you can hear the sound of helix preset 10C.
NEVER TOUCH VOL KNOB.
Preset change (e.g., 10C->10B->10D whatever), then into Stomp mode, turn on-off some of your effect chain,
Skip tuner mode and tweak the vol. but it does not change, sound level you hear stays the same.
I have tried above 4 cases 5 times each and as for vol behavior, it was reproduced.
I hope my Trial-03 helps some of you for the time being.