something doesn’t jibe here. the version listed is definitely signed and notarized – otherwise we all would be having the same issue and my support inbox would be overrun with this problem (it isn’t).
my bet is that we’re looking at two separate copies of Stacks – the one that is running is somehow older – and the copy that was downloaded is not currently running.
perhaps you have an old copy installed, and when you double click to install that old copy is momentarily trying to run (before even the installer gets going).
or perhaps there are multiple copies of stacks installed – an old copy that is running, and a new copy that is being updated?
- open the RapidWeaver addons folder ( View menu > Reveal Addons Folder ),
- remove all copies of the Stacks.rapidweaverplugin,
- Quit RapidWeaver,
- download a fresh copy of Stacks from http://yourhead.com/stacks
- unzip and double click to install
if this doesn’t work, then there is something truly amis with RapidWeaver or macOS on this machine.