Which property is it getting an AccessedNone for?
I can see it maybe happening if the Get Player Character from index 0 is trying to get a Character when the player has possessed some other kind of pawn that is not a Character,
OR,
it could happen if the player at index 0 is not possessing anything at all (though that seems like likely than the first idea I had).
I am basing these comments on what I see in your blueprint screenshot above.