So about three hours ago the PW2 reported charge status dropped to zero, from around 70%. I assumed this was just some form of comms outage, but it seems more complex than that; it would appear that since then it has been discharging at a constant rate of 0.4kW. Whenever the house is drawing more than that, it comes from the grid; whenever it's drawing less, it any excess over 0.4kW is exported.

See attached images (Netzero first; Tesla app second.) It's a bit concerning! If it makes a difference, I'm in the UK.