I was having this exact same issue and was able to fix it by removing the device, doing a factory reset and adding it back in my app as per these instructions https://support.u-tec.com/hc/en-us/articles/360058926071-How-to-Reset-Ultraloq-Smart-Lock-to-its-Factory-Settings
What hinted me to do this was that not only I was unable to lock/unlock via wifi or bluetooth, but I was also unable to manage users. When I attempted to add a new user, I got an error saying something about invalid admin or something like that (sorry, I didn’t screenshot it or jot it down) and asking explicitly to remove and add the device again. I did so and the lock works perfectly again. Thankfully it was not an actual hardware damage, but man these error messages and the utec web services in general are just awful.
Hopefully this helps someone fix their lock!