This sounds to me for sure like an issue with the unit. 
Does it happen in bypass as well or only when it‘s active?
If i were you i‘d get in contact with customer support about this.
If you can - it’s probably a good idea to provide them with some audio example or video that showcases the issue. Maybe an example of the tone you are sending in Pre-Press and what it sounds like Post-Press.
Feel free to share it here as well, then you can point support to it too.
Hope it gets sorted out quickly 