My Asus X553M laptop won't go into suspend state when using Ubuntu 18.04 LTS or 16.04 LTS with Linux 4.15.x kernel. The screen just goes blank but power does not blink to indicate suspend state. The computer won't wake up either - I will have to turn power completely off to continue. This does not happen when I select Linux 4.13.x kernel from start menu: the laptop goes to sleep and wakes up properly.
I already downgraded my 18.04 LTS to 16.04 LTS in hope that I would be able to use Linux 4.13 for longer but I just noticed 16.04 LTS is updating itself to 4.15 kernel as well.