Function _load_textdomain_just_in_time was called

Thanks for the prompt reply. Yes, indeed, it’s the Pro version on the client’s website. Unfortunately, I won’t be able to test the free version – setting up the environment would take too much time and it’s bit more cosmetical bug for me. I just wanted to clean up the debug log. This is what I got from codex:

In permalink-manager.php the plugin calls run_permalink_manager() immediately when the file loads (line 388). That instantiates Permalink_Manager_Class, which (a) registers get_options_and_globals() on plugins_loaded and (b) instantiates all helper classes, including Permalink_Manager_Pro_Functions (lines 50–109, 115–134).
When plugins_loaded fires, get_options_and_globals() runs (lines 146–162). It calls apply_filters( 'permalink_manager_alerts', array() ), so every alert callback runs before init.
One of those callbacks is Permalink_Manager_Pro_Functions::pro_alerts() (see permalink-manager-pro-functions.php (line 268)). That method calls self::get_expiration_date() (lines 166–237), which uses multiple __() translations (e.g., lines 186, 191, 196, 200, 205, 211, 216, 221).
Because those __() calls fire on plugins_loaded (i.e., before init and before localize_me() loads the text domain at init), WordPress’ just‑in‑time translation loader kicks in early and triggers the “Translation loading for the permalink-manager domain was triggered too early” notice.
To avoid the notice, either (1) defer the alert building until init (e.g., move get_options_and_globals() to init or gate the permalink_manager_alerts filter until then), or (2) ensure the text domain is loaded before those translations run (e.g., call load_plugin_textdomain( 'permalink-manager', ... ) earlier, or avoid translation functions until init).

I hope it helps and it’s not a false positive. It has helped me so far find five other sources.