Recently had the same issue of charging amperage dropping to 16A, with the 'T' on the Mobile Connector flashing 4 times. (See attached PDF for what the diagnostic codes on the body mean) I have a 2021 Model S LR. I will give the details below, but one piece of data that was eventually shared by the Tesla Remote Technician (via Service Message on the App) was that the car data log only captures the Wall Plug Temperature when it exceeds 145F. They can give you the actual temperature. Mine was 149F. If I had known this, I would have changed the receptacle much sooner.
In the previous events, by the time I got to the plug to measure with my temperature gun it was in the 110F range, so I thought it was the Mobile Connector. On 8/10/22 I changed out my Leviton receptacle - #279-S00 (It was not discolored nor looked degraded) for a Hubbell #HBL9450A 240V/50A NEMA 14-50. It is on a 6/3(18 inch run inside the wall below the breaker panel) and 50A Circuit breaker dedicated circuit. (Also torqued the terminals to 75 in-Lb as required) Recently did an 8 hour overnight charge after a long trip with no issues. I checked the temperature of the plug every hour for 3 hours, never exceeded 102F on the plug head.
The Leviton was installed and used continuously on my 2018 Model 3 from 12/2018 to 8/2021. Then for my 2021 Model S LR since then. To get to this point, had 3 separate Mobile Service Calls, they replaced the Plug, then the Body and Cable. Honestly, if they had given me the 149F on the first issue, I would have replaced the receptacle immediately. It was all covered under warranty. Bottom line, as on many threads here, use a commercial/industrial grade receptacle for EV charging. Hint: Zoro.com has great prices on the Hubbell #HBL9450A and the required wall plate (it is 2.48" in diameter, the Leviton is 2.15") it is also 1.81" deep vs. 1.0" deep for the Leviton, so you need a deep double gang box to handle the 6/3 wire, one nice feature is it has both rear and side terminals.
Hope this helps.
