It looks like Yandex is closing the connection, Duplicati is exhausting retries (attempt 5 of 5 failed), and your upload (a modest-sized dblock) never gets uploaded. Do short files (e.g. dindex) upload OK? The “Test connection” button is (I believe) just a download of a directory listing. It’s not a transfer stress test. Duplicati.CommandLine.BackendTester.exe can do stress testing, but you could check job logs as well.
“RetryAttempts” in “BackendStatistics” should count all the retries for the Rename/Retry sequence you posted. You can also infer upload retries from job Show log → Remote. If file with same size & hash is seen repeatedly being put, it’s likely a retry. You have to click on the put line to see that level of detail.
For a better view, use About → Show log → Live → Retry. For more retries, raise –number-of-retries.
Retries are somewhat expected on the Internet, but too many cause trouble. You might also have local issues such as a router or modem of some sort that needs reboot. I have to do that to mine sometimes.
Network issues can also cause slow transfers, and an Internet speed test might show if your service is working as it should. If upload is slow, your ISP might have you perform additional troubleshooting of it.