This is about a Range Rover Vogue, but as they are technically similar, here goes:
Following an issue with the exhaust oxygen sensor, even if the vehicle started in electric mode each time, when the combustion engine kicked in (usually sudden acceleration), it would not switch back to electric mode. I thought the sensor was the issue, so I replaced it and cleared the errors, however the problem persists, after switching to ICE, it doesn't switch back to electricity. There are no errors displayed on my OBD tool. After a restart, electric mode comes up, until engine kicks in, then never goes back to electric mode...
Has anyone with a P400e experienced something similar?

To conclude, it was the O2 sensor, after the summer heat was over, the car started behaving normally.