With SQL Server AlwaysOn Availability Groups, when you configure a secondary in synchronous-commit mode for read-only access, there can be data access latency.
If you make changes to your data like if you perform insert, update or delete in primary, those changes may not be visible in the secondary, synchronous replica enabled for read-only access for a certain amount of time, because writing to Log is synchronous, but not REDO. REDO is asynchronous, that is, applying those changes from Log is asynchronous.
The below video demonstrates this with hands-on example. SQLTest Tool simulates the hands-on labs for you, no registration necessary. You can practice the online hands-on example while watching the Video.