Could you try following steps to help us to find the root cause?
1. Create a file called exmancoreliblog.yes and copy it to /Users/<name>/Library/Application Support/Adobe/Extension Manager CC/Log/
2. Quit Adobe Creative Cloud Desktop Application
3. Wait a while and relaunch Adobe Creative Cloud Desktop
4. It will show 604 error
5. Goto https://creative.adobe.com/addons/my_addons to make sure you have enabled this add-on
6. Send ExManCoreLibrary.log to exman.beijing@gmail.com
Thanks,
Shuolei