I have a Sub Zero 900 and both of the freezer compressor lines (insulated and non-insulated) lines are frosting over and dripping condensate down into the unit (Never did this for the first 15 years we’ve had it). Freezer temp is -10F even on the lowest setting. Is the refrigerant over/under charged? The condenser coils are clean.
The compressor low side tubing frost line will back up into the compressor if it is overcharged, evaporator fan not running, or evaporator frosted over.