@JS1 I’ve got the xiaomi gateway working again. Don’t know why, but these are the steps I took. First, I decided to check the key, so I checked the xiaomi app on my android device. After selecting the gateway, wait for a short while, then go to the three dots, select about and then Wireless Communication protocol. I checked the key with my configuration file, all was correct (no changes made). Then I restarted home assistant, and… up and running again.
No clue why it’s working now. May be the wireless communication protocol was triggered by checking it. I really have no idea, but it works fine now. Give it a try.