I’m experiencing the same issue with my brand new Smart Lock Pro (5th Gen). I received it on Friday, but the firmware upgrade has been failing since I first tried to set it up. The base firmware is 5.0.26.
I’ve tried numerous factory resets, restarts, and setting it up with other devices, but nothing seems to work. Support has been unhelpful, repeatedly asking for the same information I’ve already provided.
I own a Smart Lock 2.0 for many years and have never had any issues with it. Earlier this year, I had to return the Smart Lock Ultra due to latch issues and poor performance. One would expect that the newer generation of products would be better, but in this case, it seems like product development is going backwards.