Have a situation getting DDR4 calibration failures 10-20% of the time on system restarts (not repowering the board, just restarting NIOS with all the block including the DDR4 controller). Happens across multiple builds. Any ideas what would cause this? For now, working around by simply restarting if there's a calibration fail, but would like to get to the bottom of this.
The intermittent failures could be due to parameters setting. I suggest you to generate a DDR4 example design then compare your design with their example design (especially all DDR4 IP parameters setting) and see if any different that will causing this problem.
And one more thing, if this is on your custom board please make sure you have the RZQ resistor connect on board.
Also, here is the checklist that you can refer to: