Thanks for taking the time to write a detailed review. If your cookies gets deleted, it's most likely a misconfiguration. To get to the bottom of this, you can visit your website, then open the add-on popup and click on the book icon to open the cookie inspector. There you should be able to see what rule-type would be applied for the cookies of your website. If you need more help, please visit https://github.com/Lusito/forget-me-not/issues/