If this means you still have the errors shown earlier, then it still looks like you have a network issue.
and the other two specifically say “Unable to write data to the transport connection”. I can’t see the timing relationship from the post, but you can see if you get transport errors before “retired” errors.
Have you tried standard network diagnostics, such as restarting all your equipment, including your computer, routers, and modems, testing upload and download speed/reliability with something else, running an Internet speed test, running a ping test to some locations, getting ISP help, and so on?
If you can do network analysis, you probably have (or could install) diagnostic tools like tcpdump or Wireshark. Duplicati has little control of low-level TCP protocol. It’s Amazon code and your Ubuntu.
Raising –number-of-retries can sometimes go through bad networks, but sometimes it’s impossible.
Live log at About → Show log → Retry can show whether you’re actually getting retries on upload.