This is a known issue with filemaker databases.
It's fairly harmless and the record with fields filled with ?'s doesn't actually exist, filemaker just thinks it does.
You can eliminate the problem sometimes by re-indexing the field in question ( I'd start with the field where you're entering find criteria).
It doesn't always work. Saving a clone of your file and then importing all your data into it will correct the problem %100 of the time as far as I know.
To re-index a field:
Open Manage | Database | Fields
Double-click the field's definition
For data fields, click the storage tab and change indexing to "off"
For calculation fields, click the storage options button and change indexing to "off".
Click OK several times until you've exited Manage | Database
Re-enter Manage | Database and follow the above steps to turn indexing back on.
Thanks so much for the quick reply. I figured there was probably a known issue on this, but I just wasn't able to find it easily in the knowledge base. I was able to re-index the field and it worked. I will keep this in my stash of fixes in case this comes up again.