What is the voltage immediately after the connector is first plugged into the car, but the amps have not gone to the max?
If the voltage starts out at ~240 and goes down to 228, that is likely voltage drop on the home's electrical system. If it starts out at ~ 228 or close that just means the voltage in your area is lower than the normal 240 volts, but is still within spec.
At my house, the voltage drops 3-4 volts, usually from about 240 to 237 or 236 volts when my wall connector hits 48 amps.
I visited a friend who lived in a rural area and I noticed that the voltage dropped from ~ 235 to 240 volts down to ~ 222 to 228 volts when my mobile connector hit 32 amps. And this was when it was connected to a NEMA 6-50 receptacle that had only 3-4 feet of #6 CU wire between the main electrical panel and the receptacle. I presumed the voltage drop was on the fairly long service drop feeding his house from the transformer, which looked to be pretty thin AL triplex service drop wire, probably #2 for the whole house.
The car will charge on voltages of 208 commercial service or 240 volt residential service, plus or minus at least 10% so it won't damage the car.
I would say any voltage drop is 99.9% NOT due to a defect in the Tesla Wall Connector. If you have any doubts, check to be sure the connections at the circuit breaker and the wall connector are torqued to the correct specifications.
See this for more information:
Voltage Relationships Based on Voltage Ranges in ANSI C84.1-2016
www.spgsamerica.com