Depends on how your group of 10 was setup, whether it is multi computer or not.

The most obvious reason to me would be that you added the extra five manually and the new five don't have FTL options set. If multi computer, then it may be because the second group are in multiple sets, so ISBoxer cannot determine the correct FTL settings, so it drops them.

The easiest way to get support for this kind of issue is to share your ISBoxer profile.