Group D8d is missing. This group is characterized by the presence of a 16-fold Sn axis. Only Sn operations up to S12 are checked for. As a result, D8d would not be recognized. However, this is a rare point-group, and its loss should not be important.
Some systems which are insufficiently near to a given point group will be assigned to the nearest sub-group. For example, if
SF6 is distorted so that two opposite F atoms are at a different distance to the other four, the system might be classified as Oh or D4h, depending on the degree of distortion. This shows up mainly in methyl groups, e.g.
neopentane, in which optimization normally stops before the angles of the hydrogens are fully optimized.