Headphones are disconnected - connected repetadely when the music stops on my iPhone in off-mode

After updating my iPhone 16 Pro Max to iOS 18 (now I have latest 18.1.1) my Sleep Headphone Headband loses contact with my iPhone when I turn off my iPhone. 

I hear ”Connected” with about 45 sec. intervals. Very annoying and disturbing when I try to sleep or it wakes me up.

I have tried the following:

1. Test

I start withiPhone on, without music (it has sfopped playing music) 2 min. No problem.

Then turn iPhone in off mode.

After 44 sec I hear ”Connected”

After 60 sec more I hear ”Connected”

After 45 sec more I hear ”Connected”

After 45 sec more I hear ”Connected”

After 72 sec more I hear ”Connected”

After 45 sec more I hear ”Connected”

After 42 sec more I hear ”Connected”

After 43 sec more I hear ”Connected"

After 48 sec more I hear ”Connected"

After 46 sec more I hear ”Connected”

After totally 13 minutes I hear ”Turn off” and the Sleep Headphone Headband is disconnected.

2. The Bluetooth settings: Forget the device: Go to Settings Bluetooth find SleepPhones in the list and select “Forget this device”. Then pairing the headphones again.

3. I have tried several apps with the same results

4. I have used a timer: Set a timer in the Clock app that is slightly longer than the length of the audio recording I was listening to. This did not prevent the headphones from being disconnected and reconnected.

5. My iPads work properly without disconnecting-connection-disconnection-connecting

6. Battery is 80%.

7. Turned off WI-Fi. No change.

8. Inactivated handoff. No change.