I ended up borrowing PCE02 from the local bike store and re-flashed the firmware. Only took 5 minutes to fix it and now I am seriously considering purchasing PCE02 box.
Same happened to me. Picked up my first eMTB today, charged up and tried updating the firmware, but it got interrupted due to weak wifi signal. Now it is bricked and only shows 'Shimano steps' logo for about 4 seconds then turns off. No chance to access PCE1. Need to book a service on Saturday.