Please contact customer support through the Nuki App (Menu > Help > Contact Customer Support) if it happens again. This will generate an error report with detailed debug information from the Smart Lock attached.
The bottom segment of my Nuki lock returned to being permanently on dimly, however before I got around to submitting a bug report the issue flipped to the top segment being on dimly and the bottom off.
I submitted a bug report to Nuki support, however before they could answer the issues disappeared after the lock auto locked for the night.