Uploading to the cloud takes a few minutes and should be done when using wifi.

Make sure that you are connected to a stable and strong WiFi connection. Slow connections or mobile connections might timeout.
Please note: check your WiFi connection - upload speed (speed test) 

Make sure that there is enough memory space on your phone. To see that enter your phone's settings and memory, make sure that there is empty memory space.

Make sure that your phone's time and date is set to automatic.