Understanding why Plasma Cut Voltage Changes

Hello, I am trying to understand why a plasma torch (PowerPlasma62i via Langmuir CrossFire with IHS & ZHC) is cutting at abnormally high voltage on the first arc of my program and decreasing at about 0.5 V/min (with fluctuations as it does so) until reaching a normal cutting voltage. This trend continued onto the next part with about 5 mins between parts. Does anyone know why this happens?

Note: this was a thick material for the current on a breaker which can thermally trip on long cuts. I am aware this is not ideal.