Some of my students in a group do not appear on the stats page

I have 14 students in a group. Only 10 of them appear in the stats section. The first 10. The other 4 are not there. When I click on the next page of stats, some appear again. So I seem to have stats for 14 students but I only see the same 10, some of them are repeated in another page of the stats. It happens with othe groups as well. I am sure this used to work before.