The Stacks plugin is made by YourHead Software.
If you have any issues using Stacks you should contact YourHead directly using the following email address: support@yourhead.com or support@yourhead.zendesk.com
YourHead also runs a Discord channel that you can ask questions on:
Please note in order to get support via Discord it’s required to sign up for a Discord account.
And finally you can submit a support request via a Form here: