I also saw the Valydate web site was down. A little research shows why https://semiengineering.com/tag/valydate/ They are now part of Mentor Graphics.
The 410c and 820c boards have been through all of the checks that Valydate could have possibly have done. They had access to the IBIS and other models for checking everything that can be checked at pcb layout time. You can get the IBIS models from Arrow and gun them on your own CAD system.
I had concerns when you designed and built your own board, critical to correct operation of the chipset is the power delivery and signal integrity. I hope I pointed out all of the things you have to check when I wrote the design guidelines.
Does your board work if you solder on a 8GB eMMC part? However based on the failure to boot from SDCard, I would guess that the problem is in the Power Delivery Network (PDN) layout.
No longer a Qualcomm employee
searching for new employment.