I've recently had an inverse sort of problem: The PWs started grid charging anytime the SOC was below the reserve, although I have never enabled grid charging and the app showed that grid charging was disabled. At first I suspected this might be related to our recently installed Wall Connector and my consequent use of NetZero automations to change the PW reserves each night. However, more experimentation showed that the grid charging was only dependent on SOC versus reserve. I had no response from email or chat, but on Juneteenth morning my phone call was promptly answered. Once I got him to doubt that grid charging when it is explicitly disallowed is not "working as expected", he asked his supervisor and subsequently apologized for his "mix-up".
Anyway, simply toggling grid charging from their end did not stop the behavior, so they tried setting my system configuration to grid charging not permitted, and that seems to have stopped the behavior. If next winter when my solar can't keep pace with the heat pump, perhaps I'll have to revisit the question of whether to use grid charging. Maybe I'll have to get them to change the system configuration back, but I'll worry about it then. Likely the firmware will be completely different in 6 months anyway. At present my Tesla app lists grid charging as "Restricted".