Right click on screen and click on Inspect, this will open the browser's inspect window.
- If the message there is Refused to set unsafe header "user-agent" the uploading activity is still on and you can wait for it to be completed.
- If the message there is net::ERR_TIMED_OUT or net::ERR_INTERNET_DISCONNECTED your internet connection is unstable. Please, contact the IT team to solve this issue.
P.S. Discover Azure Integration, the easy way to upload files from any Salesforce record to Azure. Find it on AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=c9e71bd6-5bab-4182-a461-b82d4f971183