I too have the same issue for an Ioniq 5 ( Relevant Post: FMM003 OBD unavailable during AC charging ). However, for me, the new EV Charging feature in the new firmware completely disables my HUD during driving while not providing any information when AC charging.
While a reply on my post suggests that the car is the one controlling OBD data while ‘charging/off’ , I believe that it is the actual Teltonika firmware that stops OBD polling while stationary since a normal ELM OBD dongle can poll OEM data just fine when stationary or during AC charging.