Critical Issue
In the FIFO MegaWizard Plug-In Manager, on the Parameter Settings page, if you turn off Show-ahead synchronous FIFO mode and select MLAB under What should the memory block type be on the Rdreq Option, Blk Type, and then on the Optimization, Circuitry Protection tab, select No (smallest area) under Would you like to register the output to maximize performance but use more area, the generated SCFIFO behaves incorrectly.
Under What should the memory block type be on the Rdreq Option, Blk Type tab of the Parameter Settings page, select a memory block type other than MLAB (that is, select Auto, M9K, or M144K).