No Bootable Device despite Windows Boot Manager

So I shutdown my windows 10 based Inspiron-15 5000 after a normal day's work. When I turned it back on again the next day, instead of booting into Windows, it opened a dignostic check which it passed but never booted into windows. Btw I have a SATA SSD which holds my windows and an HDD for data. I tired  disabling secure boot and making sure UEFI was checked. I even resetted the BIOS to factory setting but nothing worked. It also said "No bootabe device" despite the F12 menu showing "windows boot Manager". I looked up the problem online. A solution fixed the problem by adding another boot sequence named "Windows boot manager" which file path: /EFI/BOOT/BOOTX64.EFI. This solved the problem. But I still dont get why the problem came up the first place. Is my SSD faulty? If not then what is it? Thanks!