I will try it also, I could not boot mx18 or latest antiX on my complicated chromebook with custom build & upgraded bios that allows installation Linux on it. It is a long stretch but this is how I managed to 'fix' the issue in my case:
I booted MX18 on another, normal computer and installed new MX18 on it. Then I created snapsot iso of that newly installed MX18. I then burned that snapshot iso on the USB stick with dd and this USB stick booted normally on my complicated chromebook with custom bios. Interesting!
Later I have learned that bios was expecting efi file somewhere else and another solution is that i can in bios browse to the efi file location on USB stick. Anyway, my case is quite different and probably not relevant but I though to mentioned it anyway.