I tried running 'chroot /mnt /usr/bin/os-prober in the installation system, and got a message to stderr /run/lvm/lvmetad.socket: connect failed: No such file or directory WARNING: Failed to connect to lvmetad. Falling back to internal scanning. Does this account for not finding the Windows system on /dev/sda2 ? It probably doesn't account for why my machine is different from the others that we have tried, though.