EFI fast mode should be enabled. If you rarely upgrade RAMs/SSD then you won't notice anything different. Without fast boot, nvme drives 2TB+ and 128GB+ RAM takes too much time to initialize.Fast startup created issues for me as well, mostly to get RAM stable... So I disabled it from UEFI. Actually there was another fast boot setting "mrc fast boot" under ASUS UEFI settings... Disabled both. And I mean 2 different fast boot settings in UEFI. Fast boot skips RAM checks I think to make boot time slightly faster, but I don't think its worth it to trade off stability for few seconds faster boot honestly. Based on my own experience, I'd disable it every time.