I have recently started a trial of Mathematica 126.96.36.199 for use in developing a new 3D game engine.
The software works well, aside from the odd issue of not being able to save to Wolfram Cloud. I can create files on the Cloud website itself just fine. After creating a notebook on the cloud, I can then open the file from the cloud locally. What I cannot do is save the file or save a new file to the cloud. I will get a popup window called 'Wolfram Cloud Activity' with the filename and next to it, 'Waiting...' while both Mathematica and the kernel take up 50% CPU each (adding up to 100% CPU). Both processes will just hang there indefinitely with no network activity.
Oddly enough, I can use the Cloud API methods to save the notebook (as a new, unnamed file). I can also manually upload the file itself to the cloud. The only thing that does not work is saving to the cloud via the GUI (File -> Save to Wolfram Cloud...). The process will sit at 'Waiting...' taking up CPU until I cancel the "upload" manually.
This is a minor issue at best, but it would be nice to be able to use the in-program feature to save to the cloud without having to manually upload files.
My machine is a Macbook Pro 15" Touchbar Late 2016 model running macOS 10.12.4 if that helps.
I would recommend contacting support.They should be able to help you with this issue.