Unless a recent Windows 10 update screws up the UEFI bootloader and points the loader to the second partition which is incidently used by OSX and prevents booting Windows (well, it fixed an issue on Dell laptops with Windows, which suprise suprise is where most Microsoft PC’s are supplied from). The silly recovery tool wont allow you to mount the eFI boot partition in R/W mode so you cannot fix it yourself (EFI boot requires correct partition UUID). Windows 10 update killed bootcamp option for me, now I triple boot with Linux and Haiku.