That’s the correct behavior: the license key input box should always appear empty. This is because we don’t store the license number in Slicer (it is passed to TotalSegmentator, which authenticates with the server and stores the authentication result).
The screenshot shows that the license is successfully authenticated:
License has been successfully saved.
License has been successfully set.
After that you included some logs that showed an error. Maybe your firewall or proxy server interfered with the authentication. But if you have already set the license successfully once then you don’t need to worry about it, it should work well.