The ID numbers in Family Tree Builder 7.0 are now set to be the exact amount of people in your family tree. For example, if you delete a person with ID number 4, then all the people in your tree will be re-indexed, and this ID number will be given to the next person in the list. The total amount of ID numbers will now match the exact amount of people in your tree.
This is different than how the ID numbers worked in FTB 6.0, so after upgrading to FTB 7.0 it is possible that the ID numbers of certain people in your tree will have changed.
You can change the ID numbers back to the old (FTB 6.0) format. Open Family Tree Builder on your computer, select ‘Tools’ on the upper menu bar and click ‘Options’ > ‘General’ > and use the “Choose IDs of elements in your project” option.