The following are the two primary reasons that you may be unable to find these people:
DESCENDENCY: When you import your GEDCOM into OneGreatFamily, the Genealogy Browser™ assigns the first person listed in the GEDCOM as the anchor (or starting person) and displays any ancestors for that anchor. It is possible that the people who appear to be missing are descendents of the anchor. If you want to view descendants of an individual, click on the individual in the Starfield, and then click on the descendency icon(located on the icon bar of the Genealogy Browser™). You may then make a new Anchor
from any of the individuals shown in the descendency view.
NON-LINKED GEDCOM: The Genealogy Browser™ only assigns one anchor when importing your gedcom. If the information in your GEDCOM contains more than one group of non-connected ancestors, it may appear that the unconnected group of ancestors are missing. Since all individuals are imported from the gedcom, you can use the search feature to search for the unconnected ancestors.