Today, I received:
$ sudo apt-get update && sudo apt-get upgrade # [...] Err:22 https://xpra.org/beta xenial Release.gpg 404 Not Found # [...] E: The repository 'https://xpra.org/beta xenial Release' is no longer signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.
Thanks, re-pushed. (not sure why it got wedged)
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2208