I haven't used Carbon Fibre PETG but I think @Redback is correct about the using a hardened steel nozzle. A bronze nozzle wouldn't immediately cause the issues you're seeing but over time the abrasive the material will wear it away.
For regular PETG I print with the fan off for the first 4 lawyers then 25% speed for the rest of the print, 70° bed, 230° hot end and I print on regular old masking tape to stop it taking chunks out of my glass bed. I'm yet to have a failure. Maybe the masking tape is the key or perhaps carbon fibre infused filament is just more sensitive to settings?