chances are you didn’t upgrade to the latest version of SU21 back then, it’s a chromium issue.
SU21 won’t be supported by the 3d warehouse next january, so moving to 22+ might be needed in the long run.
If you still can’t access it through the integrated tool, you can also still use it in your browser and download directly. Since SU files are now the same regardless of the version (21+ is the same) this method will work for a long time.