Well I'm baffled by that because Lubuntu 16.04 and Mint 18 are both based on Ubuntu 16.04
I'd have to check if they were using a different version of GRUB, and there's always the slight chance it's that Mint are loading different modules (but I doubt it) .. so all I can think of is comparing the grub.cfg from a Mint install and a Peppermint 7 / Lubuntu 16.04 one.