Heat is causing the distillate to be peramable and oxygen is moving in. I think it’s the overlap of BP that other cannabloids are taken in during distillation or micro fats and lipids still remaining. I’m not sure if you can do this with carts but maybe using the air sealed plastic cap for the bottom of the cart on it while doing this process. I would take the carts and place them in a vacum oven immedatly after your fill. Have the carts completely diagonal in a holding tray suitable for heat. Have your oven heated up to 100f. Wait for vacum show stable heat. open your vacuum valve at a slow rate once you get to 29.5 slowly release it and any oxygen should be out.