There is a bug with mod wheel that was haunting me for some time and I finally caught it. Looks like it’s random but after assigning mod wheel to any parameter and then assigning other parameters it can assign itself in non-visible way to last assigned parameter. Then it controls value from min to max (without respecting settings) & can not be unlinked from mod wheel list of assignments itself because it’s not visible there.
Please see this gif as it shows it better than words:
Vital 1.5.5 VST2