Certainly this iCloud upload being stuck bug is frustrating. My method to resolve it is as follows: Launch Activity Monitor, click on the CPU tab at the top, look for the bird process in the Process Name column, select it, and stop it (kill it) by clicking on the Stop icon on the tool bar (the one with an X inside a circle). You will noticed that the process id number listed in the PID column changes after a couple of seconds, which indicates that the bird process has been restarted by the system (The bird process is responsible of the iCloud background file synchronization). Most of the times this solution will work. If stopping the bird process did not solve the iCloud synching, then perform a full shutdown/restart of your computer. This is the ultimate fix that has always worked for me thus far.
Topic:
App & System Services
SubTopic:
Core OS
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