Later EDIT: Please contact me directly via email (gabrielivanica@gmail.com) with any question you might have regarding the addon. For more direct ways of communication (if needed) I will send you an email after you contact me first.

P.S If the addons shows that "Current Sessions" entry most probably works as it should but might not work as you expect.
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I don't really understand why it would not be saved. I mean there's that tab called "History" where you should find the most recent saved sessions.

At this point the auto-saved function creates a new session entry only when the browser starts. Then every 60 seconds (or whatever you set) the same session will be overwritten. If you close the browser during those 60 seconds when you open it again you should find that specific session saved in the History tab.

Only manually saved sessions are stored in the Sessions tab since those are stored as bookmarks while the auto-saved one are stored in internal memory and can will be automatically deleted when the storage (that you also set) is full.