xiaomi door and motions sensor timeout unavailable problem
Some Xiaomi sensors only send data when you actually open the door or close the door, or when they see motion. The sensors also send motion clear after 1, 2, 5 10, 20 and 30 minutes. After that, it will stop broadcasting data, till they see motion or till you open the door. So, these sensors can have a long time without sending any data (e.g. during the night).
I think the Bluetooth integration is determining an interval in which it expects data, based on previous messages (interval). If it doesn't receive data within this time, it will become unavailable. Unfortunately, these sensors stop broadcasting after 30 minutes,
https://github.com/home-assistant/core/issues/87296 