Device update triggers factory reset and completly locks user out
Called both android and huawei support. Neither of them was helpful. Both insisted that this shouldn't happen, althou the google support said he once had a similar case from a huawei consumer. Both suggested to delete the phone from list of devices in the google account. That didn't work and neither could tell why it didn't and how it could have helped.

Huawei accepted it as a repair case. The phone is still in the warranty period, so i hope for a replacment phone.