I have an iPhone 6s running on iOS 11.2.6 and an iPhone 4s running on iOS 9.3.5. The 6s seems to work perfectly in the background, but the 4s keeps suspending instantly and it can not be awaken by the 6s and wont receive a single message (also not publishing). Both publishing and subscribing running on BLE and background mode is allowed on both devices. Bluetooth central and peripheral capabilities are enabled on both devices. Background mode should work on iOS9? If yes, what could be the problem? Thank you in advance for your help.
Update: I've also tried it with an iOS 10.3.2 device and it seems that background mode works between iOS9-iOS10 in both directions, iOS10-iOS11 both directions, but iOS9-iOS11 only in iOS9-->iOS11 direction.
I have an iPhone 6s running on iOS 11.2.6 and an iPhone 4s running on iOS 9.3.5. The 6s seems to work perfectly in the background, but the 4s keeps suspending instantly and it can not be awaken by the 6s and wont receive a single message (also not publishing). Both publishing and subscribing running on BLE and background mode is allowed on both devices. Bluetooth central and peripheral capabilities are enabled on both devices. Background mode should work on iOS9? If yes, what could be the problem? Thank you in advance for your help.
Update: I've also tried it with an iOS 10.3.2 device and it seems that background mode works between iOS9-iOS10 in both directions, iOS10-iOS11 both directions, but iOS9-iOS11 only in iOS9-->iOS11 direction.