Welcome to AC forums. We're probably going to need a bit more information to help you with your issue. To reply to this thread please create an account. This link will help you do that...
https://forums.androidcentral.com/ask-question/409154-join-android-central-community-new-post.html
Meanwhile,
When it turns on does it connect to anything? Is there one specific device that it connects to, you just randomly find it on, it doesn't matter the device, if it is one that you've paired to it will suddenly connect...
Do you have an app or service like Tile, that has permission to turn on your Bluetooth? On my Samsung, push and hold the Bluetooth toggle in the quick settings menu>use the 3 dots to find Advanced>under Advanced Bluetooth control history, this will show you anything that has turned on your Bluetooth recently.
Let us know what you find on those two and we will be able to help you better.