Perhaps you or some other user(s) are inadvertently creating new records without realising? See if you can work out when/how this is happening. If you capture a bit of metadata when records are being created it will help.
Couldn't it also be the field you are sorting on doesn't have a value in it for the record? Make a field in the sub summary part a button with a simple GTRR. It will take you to the blank record