Since updating to 2021-04-09 Experimental (on Linux) get non-blocking socket error

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

And indeed - disabling the mail alert cures the problem.

The forum topic you cited fixed their email through options changes, if you wish to pursue that sometime.