I've been running Windows 10 alongside Ubuntu and Windows did an update that removed the GRUB loader. After running BootRepair, the message displayed changed to "An operating system wasn't found …". Then I ran Gparted and it showed that my Ubuntu partition was unallocated.
At this point, I don't know what to do and if I can recover my partition. The URL link generated by BootRepair is http://paste.ubuntu.com/18088419
Thanks for your help!