You might try getting the ABS system bled using the scan tool just to be sure, and have the calipers rebuilt to make sure they are working as intended.
Ice mode results in a hard brake pedal with less travel and limited braking force, then when the car reaches a lower speed the braking will return to normal with the pedal going down further. If you quickly initiate braking with any steering input above a certain speed, it will also limit braking in a similar manner. IME, this isn't ice mode but it's the same idea and happens for the same reason, ABS is trying to keep the car from spinning.
Your '18 ZL1 is unfortunately one model year before the ABS system was revised to minimize the occurrence of ice-mode when using other than OEM tires, the fact you're running 3Rs which exceeds OEM tire grip and actually using that extra performance is likely the cause if it is indeed ice mode. You can get a '19+ EBCM from a car with the same options as yours, which will help, but might not completely eliminate the issue, or you can get a ZL1 1LE which doesn't have ice mode, afaik... Sounds like you need a 1LE!
