Behavioral simulation models are not supported for the built-in FIFO configuration.
You should generate a structural model when using a built-in implementation. If a behavioral model is generated, a FAILURE scenario will be generated within the model and the simulation will stop with a message to use structural models for built-in FIFO implementations.
Structural simulation model is UniSim-based model generated along with the core.
To generate a structural simulation model, open "Project Option" in the main CORE Generator GUI. Click the Generation tab, and change simulation files from "Behavioral" to "Structural".