Strange result when using plotting antenna pattern with CustomAntennaElement

I have designed an antenna in CST MW studio and want to import the antenna element into Matlab. I am using CustomAntennaElement in the Phased Array toolbox to do this while following this guide. https://www.mathworks.com/help/phased/ug/antenna-array-analysis-with-custom-radiation-pattern.html

The output pattern that I get after importing it into Matlab is close to what I expect except for this weird result on the z-axis. There is some weird spike at the +/- z-axis while it should be a smooth transition. I have also attached a surf() figure of the output of pattern() function I used to plot the pattern of which I don't see anything wrong with.

Code I used

clear;
clc;
data = importdata('29ghz_3d_pattern36090.txt');
datas = data.data;
theta = datas(:,1); phi = datas(:,2); gain = datas(:,3);
theta = 0:360; phi = unique(phi); 
fc = 29e9;
datascopy = datas;
patternphi_theta = [];
len = length(theta);
startind = 1;
endind = 360;

N = length(phi);
for i = 1:N
    rowvect = gain(startind:endind);
    rowvect = [rowvect; rowvect(1)];
    patternphi_theta(i, :) = rowvect;
    startind = startind +360;
    endind = endind+360;
end
freqVector  = [29 29.1].*1e9;
% change phi and theta around for MATLAB coordinates
antenna = phased.CustomAntennaElement('FrequencyVector',freqVector, ...
          'PatternCoordinateSystem','phi-theta', 'PhiAngles',theta,...
          'ThetaAngles', phi, 'MagnitudePattern',patternphi_theta,...
          'PhasePattern',zeros(size(patternphi_theta)));
      
[pat az el] = pattern(antenna,fc,'CoordinateSystem','polar','Type','directivity');
surf(pat)
shading interp

figure
pattern(antenna,fc,'CoordinateSystem','polar','Type','directivity')
grid on