This is a known issue with filemaker: Phantom Record, damaged file message, Recover can't detect a problem
The record with the ??? doesn't actually exist but part of your filemaker file thinks it does. You can't delete them either. You can fix the issue by re-indexing the affected field. Since it can be difficult to figure out which field to re-index, the simplest approach is to use the Save As.. action with the clone option to save an empty copy of your file and then import all your data from all your tables into this clone. The import process rebuilds the indexes of all your fields and you shouldn't see any more fields with question marks.
This is one of many bugs that can be found in the Known Bug List here in the forum.
This list can also be downloaded for free as a filemaker database for easier searching from: