My SmartLockUltra works great with the keypad pro (fingerprint) and the App with Bluetooth. Much better BTW from the opening/closing mechanism as the former locks as the universal cylinder and the speed is much better now.
After activating Wifi and MQTT my iOS App can not connect anymore to the SmartLock. Wifi seems stable and working, but my App can not connect anymore (no matter if I am connected with my iPhone to WLAN or not).
I am still getting MQTT updates if I am locking or unlocking the door in my iobroker instance. So WLAN and MQTT works on the Ultra. But I am not able to connect for config changes anymore to my smartlock with the app.
Check if the phone can connect to the lock via Bluetooth (Phone in flight mode, with Bluetooth active).
If that works restarting the App several times (or the phone) might help
The connection info screen inside the Nuki App might also give you more information about the state of the locks server connection.
If Flight Mode works via BLE the BLE connection to the lock should also work without, you just have to wait longer until the App gives up and falls back to BLE (>~10s)