I’m looking mostly at the 401 (Unauthorized), though it’s odd that so much else is allowed.
I’m also hoping you don’t have any sort of network proxy that might be interfering with this.
So acting like a hang? Do you have timestamps on dev tools relative to the time of stop?
You can add log-file advanced option at some log-file-log-level to see progress. Information or Retry would be good for starters, but there are also very detailed ones.
About → Show log → Live → <level> may also help if it doesn’t fail due to network issues.
What Duplicati version? What type of backup Destination? Sometimes these may also fail.
Did your backup run for long enough to get some uploads, or not run long enough for any?
There is a BackendTester which you can use with URL of an empty folder for better tests.