In real life, we have a strong expectation that the future can't affect the past, but in the Newcomb problem we have pretty good evidence that it can.
In the standard formulation (a perfect predictor) one-boxers always end up winning and two-boxers always end up losing, so there is no issue with causality, except in the mind of a confused philosopher.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)