When comparing values to NaN, MATLAB always returns false. For example, the following code displays other value even though it compares NaN to NaN:

x = NaN;
switch x
    case -1
        disp('negative one');
    case 0
        disp('zero');
    case 1
        disp('positive one');
    case NaN
        disp('NaN');
    otherwise
        disp('other value')
end

Rewrite your code so it does not compare a variable to NaN. For example, you can rewrite the previous code like this, using isnan to determine if the variable is NaN:

x = NaN;
switch x
    case -1
        disp('negative one');
    case 0
        disp('zero');
    case 1
        disp('positive one');
    otherwise
        if isnan(x)
            disp('NaN')
        else
            disp('other value')
        end
end