What could cause SQL Server to deny execution of a SP at first, but allow it later with no privileges change? A user (Windows login) just complained he was denied the execution of a procedure. I went to check and verified he had the privileges to execute it. I didn't change anything (and right now I'm the only one with admin privileges do to so if needed) and after two unsuccessful attempts he tried to run the SP for the third time and it worked.
I have XE configured to catch error messages and it captured twice the error code 229:

The EXECUTE permission was denied on the object 'storedProcedureName',
database 'databaseName', schema 'schemaName'.

Is there any situation where this behavior is expected?

Microsoft SQL Server 2014 (SP3-CU-GDR) (KB4535288) - 12.0.6372.1 (X64)
If the Windows user account was added to an Active Directory (AD) group in the meantime, and that AD group had permission to run the procedure, then that could create this scenario where a user gained access to a procedure with no changes within SQL Server.

Also get the network admin to check if the user logged off and on again. Group membership only gets assigned at logon so if the user was added to a group and had not logged off he would not have had that group membership in his token. -  Spörri

Related Q&amp;A: How do I assign an entire Active Directory group security access in SQL Server 2008?