Since updating a Duplicati instance on a Linux system to the 2021-04-09 Experimental release I get the following error message every time a backup runs.
2021-04-22 02:18:06 -06 - [Warning-Duplicati.Library.Modules.Builtin.ReportHelper-ReportSubmitError]: Failed to send message: System.IO.IOException: Operation on non-blocking socket would block ā System.Net.Sockets.SocketException: Operation on non-blocking socket would block
The backup seems to complete fine - just the puzzling error message.
Further testing suggests that it may be related to the option to send a mail message after backup. If so, this may be related to an issue reported by another user in December 2020