How can I debug error during fast startup?

I’m trying to make a system with WoA, and have a problem on fast startup procedure. It seems fast startup doesn’t work properly, but I cannot confirm that because it does not emit any error or BSOD even when I attach the system into windbg with serial.

So when I check some feeds and I found that fast startup functionality disable the BSOD on the boot sequence, so I cannot see any BSOD even if there are bug or error, am I right?

Then, do anyone know how can I debug the system during fast startup procedure?

Thanks,