The adapter should not be altering the charge rate. First thing I would check is if reduced charging rate is configured in the car’s settings.

 

One classic method to tell whether the charging power issue is caused by the charger or the vehicle is to try different L2 chargers, ideally one with a J1772 plug and one with a NACS plug (if you can find one). If those are rated for 6 kW and you are still only seeing 4.2 kW that points to a vehicle issue. If you see higher power (kW) on the other L2 chargers that points to the L2 at your building.

 

First, a little technical correction. Charging speeds are stated in kilowatts (kW), the quantity of energy used is measured over time and is stated as kilowatt hours (kWh), as it is with your utility bill. I don't mean to be pedantic about it, just that it helps to accurately describe terms to be understood clearly.

In the EV settings on the infotainment screen settings, there is a setting that can reduce the AC charging speed to 90%, or 50% as I recall. If this was set, of course AC charging speeds would be reduced.

Poke around the settings to see if it was set to lower the charging speed.

 

Yes, change the AC charge rate in the settings.

Select EV on far right of home screen to get there.