It sounds like the song that is playing every time you connect to a Bluetooth device is the most recently played song on your device. When you connect to a Bluetooth device, the music app on your device will automatically resume playback from where you left off the last time you used it. If the song that is playing is not a favorite or one that is first on your download list, it is likely that it was the last song you played before disconnecting from the Bluetooth device.
One solution to this issue is to make sure that you pause your music or change the song before disconnecting from the Bluetooth device. This will ensure that the music app does not automatically resume playback from the same song when you reconnect.
Another solution is to change the settings in your music app so that it does not automatically resume playback when you connect to a Bluetooth device. This option is usually found in the settings menu of the music app.
If these solutions do not work, you may need to reset the Bluetooth connection on your device. To do this, go to the "Settings" app, select "Bluetooth," and then tap the "i" icon next to the Bluetooth device you want to reset. From there, you can tap "Forget this device" to reset the connection. After resetting the connection, you will need to pair your device with the Bluetooth device again.