Supreme Leader Snoke is a powerful user of the Force, and he is shown to be able to initiate telepathic connections between two people who are strong in the Force across great distances (among other powers).
But why didn't he sense what was going to happen in the Last Jedi?
Snoke asks Kylo to kill Rey since she wouldn't join the First Order. Kylo seems to get ready to kill Rey, but as Snoke keeps talking, Kylo takes control of Rey's light-saber (which was sitting by Snoke) and kills Snoke with it.
Snoke even says (just before this event happens) that he is able to sense each of Kylo's thoughts. This was such a significant event and change in the plans (Snoke's plans), why wasn't he able to sense what was happening right next to him?