An expunged criminal record means that the record was removed from government archives that are accessed by the public. But the government still keeps a record in their private archives. So, if you apply for certain government jobs, you can bet that it will show up in an FBI background check. For example, it will show up if you apply for a job that gives you control over vulnerable people, such as teacher, child care, elder care, nursing, or doctor. It will show up if you apply for security related jobs, such as policeman, fireman, air travel, or for a government security clearance.
And, the expunged record can still show up in a background search run by a private company. The reason is that the criminal record was public information right after the arrest or conviction. It took some time for you to go through the legal process of getting the record sealed. In the meantime, a company like BackgroundSearch.com (and others) may have already put the court’s public record in their private database. Once there, it is there forever.
An expungement will apply to the government records only, but the private database can still report the information. You can try to contact all the private background search companies and ask them to remove the information, and some of them will comply.