Same problem here. I asked someone at the property to replace the batteries, no changes to the configuration whatsoever. The opener then kept saying that the PIN was wrong, either with the right one (I know it’s the right one because I’ve been using it for a year and I never changed it) or trying with 0000 as suggested here. I also started receiving warnings in the app that the battery level is critical (not true, since these are brand new standard batteries), and that the battery level for the door sensor and for the keypad are critical (again not true, since I never installed any of these).
I contacted support and after trying a few suggestions there was nothing we could do but a factory reset, which requires being present and connect via Bluetooth. Then I had to reconnect the Opener to the bridge and all problems disappeared.
This is really disruptive and inconvenient. I could not get to the property for weeks, and could not send new invitations to any of my guests in the meantime because one needs to be physically present and connect via Bluetooth to reconfigure everything. So we had no option but to fall back to appointments to deliver keys until I had a chance to visit.
The point of using a wireless opener and wireless lock is to configure them once so that we can later manage everything without being physically present. We cannot rely on a device that loses its configuration when replacing the batteries. I was cut off from changing anything in the Opener or from accessing its configuration via Nuki Web. Please Nuki review this bug and fix it. It is obviously a major blocker for many of us.
I also had huge problems with the power pack for the Smart Lock failing within a year. I really like Nuki products, but batteries and battery replacement have been sources of very serious problems for both devices. Please make sure that anyone can replace a battery without affecting usability and configuration. It is really frustrating having to reset and reconfigure everything when batteries fail and having to later create new initiations for all users from scratch.