Hi Yao w!
I've downloaded your H5P Interactive Book activity and uploaded it to my local Drupal test site. I confirm what Sara said, it's definitely not a Moodle issue but an H5P issue.
There are actually 2 problems with your activity.
1.- If you want the student to find all the "o"s on your image, then you should use the "Find Multiple Hotspots" H5P activity, not the "Find the Hotspot"activity, which as it name implies is suitable for finding just ONE hotspot! Note that "Find Multiple Hotspots" is not the same as "Image Hotspots", which is something different. All this is a bit confusing.
2.- Unfortunately, currently the "Find Multiple Hotspots" H5P activity is not available within the H5P Interactive Book activity. This is the list of the currently available activities in Interactive Book. You will notice that the "Find Multiple Hotspots" activity is missing.