Stuck in "Connecting" but already connected

Doing a firmware update of our peripheral from Android works fine. However on iOS the DFU process is stuck at a very early phase.

We are using Secure Buttonless DFU with our own control characteristic.

We first connect our device, then we hit a "Start DFU" button. On Android the lib now writes to the control characteristic which will reboot the device into the bootloader. On iOS basically nothing happens. We get one single log entry. The device stays connected and that's it.

dfuStateDidChange(): Connecting

I think the lib should not try to connect, because the peripheral is already connected. Using the debugger I can see, that things go wrong in DFUPeripheral.start().

        // Set the initial peripheral. It may be changed later (flashing App fw
        // after first flashing SD/BL).
        guard let peripheral = centralManager
            .retrievePeripherals(withIdentifiers: [targetIdentifier]).first else {
            delegate?.error(.bluetoothDisabled, didOccurWithMessage:
                "Could not obtain peripheral instance")
            return
        }
        self.peripheral = peripheral

        if peripheral.state != .connected {
            connect()   // <<<<<<<<<<<<<<<<< We end up here, but shouldn't
        } else {
            let name = peripheral.name ?? "Unknown device"
            //....
        }

For some reason peripheral.state == .connected while still in our code. But if we enter library code the peripheral which is received by centralManager.retrievePeripherals is not connected but still has the correct name, so it seems to be the correct peripheral.

Does anyone here has some insights on that behavior?

DFU Bootloader version

SDK version: SDK 15.3
Bonding used: no
Library version: 4.9.0

Device information

Device: iPad 7th gen
OS: iOS 14.3

NordicSemiconductor / IOS-DFU-Library

Stuck in "Connecting" but already connected #403