Although developer input on the action here would help, the location looks like it’s in .NET, which limits what Duplicati code can do about it. Web search shows that some people have found that networking change avoids this. Are you familiar with how virtual networks can be set up? I’m not.
Another avenue would be to try to sanity-check the network with a performance test, for example
Check Your Home Bandwidth (by Backblaze, but not actually for B2 – it still might be informative)
You can also try command line testing. Get your target URL using GUI Export As Command-line.
Duplicati.CommandLine.BackendTester.exe can do an automated test. Point it to an empty folder.
Duplicati.CommandLine.BackendTool.exe can run manual tests if you prefer that, e.g. try the get.