Contact record cannot be searched/found in CRM

Contact record cannot be searched/found in CRM

We have a system setup to assign a unique 6-digit ID to our customers, people seeking training.

We've created and integrated a Zoho form for people to create an ID if they do not have one.  This creates a Lead in the system that automatically converts to a Contact using a workflow rule.  This has worked without issue in hundreds of cases. 

However, we just had one individual use this process and something about the record seems broken.
  1. We cannot find the contact by searching for the unique ID in the system
  2. We cannot search for or connect the contact record to any other modules using the unique ID, or even by using the full contact name or last name.
We have many others who have worked just fine, but cannot figure out what happened with this outlier to prevent it from happening again.

Any thoughts?