Earlier this year I was in Japan and Korea. Now I'm back in my home country. However, when I was in Korea the "scan" machine before going to luggage inspection, right before accessing the boarding gates made a weird "alert" sound. It has happened at least twice already, but both times the officer just handed me back my passport and didn't ask me anything. They just made sure I looked the same as in the photo.
When I was checking out of Japan, before going to the boarding gates, when the officers scanned my passport, they all looked at each other confused but never looked at me or asked any question.
I'm wondering if there's something wrong with my passport and what it could it? I'm a little concerned even though I've never been asked anything whenever this happens.