I'm getting a spinner or the upload process won't complete
Check your network
It is possible you or your organisation are blocking access to Dash. Please read this article for information on how to whitelist Dash on your network. A good way to test this is by attempting to recreate the problem using a different network (e.g. on your home wifi or temporarily hotspotting to your phone)
Try uploading using a private browser window
This will rule out any browser plugins or cache issues that may be causing problems.
If this fixes the problem you should:
Clear your browser's Dash cache - here's how
Disable browser extensions - turn off each extension one by one and repeat your download in Dash until the download works and you identify the offending extension. A good place to start is with ad blocking extensions.