Hello Markus,
Freddy will keep a ticket closed only if it is highly confident. That is, it has to be at least 90% confident.
Also, Freddy keeps learning from the following events :
1) When an agent manually reopens a ticket after Freddy kept it closed - This is a feedback that similar tickets should be reopened in the future.
2) When an agent closes a ticket that Freddy reopens - This is a feedback that such tickets should remain closed in the future.
Please use this link to check out Freddy's confidence level to keep a ticket open or closed. https://thankyou.freddyproject.com/
Also, I hope you have configured the thank you detector as mentioned in this article by modifying the Observer rule.
https://support.freshdesk.com/support/solutions/articles/50000000040-setting-up-the-thank-you-detector
You could create a custom ticket list view that shows all your closed and resolved tickets by using only the status filter and then saving that view. By doing so you can keep an eye on your closed or resolved tickets.
Please write to support@freshdesk.com if you have any issues or queries and we'll help you get it sorted.
Cheers!