Code correct? - signrank testing

Hi.

I want to compare two conditions of my dataset using the signrank function (data distribution is not normal). The data ("outputmatrix2") is threedimensional (pixels-timesteps-conditions) and unwanted pixels are set to NaN- which would be all but approximately 80.

Unfortunately, in almost every timestep, I get significant differences between the two conditions, even before stimulus onset (see attached image, "0" on x-axis is stimulus onset, an asterisk above the 2 graphs indicates significance with p<0.05).

I wonder, if my- pretty primitive- code is correct? Or maybe anyone has any other suggestions? Thx!

% settings
from_plot = -20;  to_plot = 200;
condA = [19];            
condB = [23];

clear cond2b cond1b A A2 A3 B B2 B3 AAA AA C D AAA2 D2 C2 AA2 p2 indeks2

% get rid of NaNs
A = nanmean(outputmatrix2(:,:,condA),3);
for j=1:size(outputmatrix2,2) %frames
    A2 = A(:,j);
    A2 = A2(A2==A2);
    A3 (:,j) = A2;
end
B = nanmean(outputmatrix2(:,:,condB),3);
for j=1:size(outputmatrix2,2)%frames
    B2 = B(:,j);
    B2 = B2(B2==B2);
    B3 (:,j) = B2;
end

% testing
for jj=1:size(A3,2)
    [p2(1,jj),h2(1,jj)]=signrank(A3(:,jj),B3(:,jj));
end
% create fancy asterisk-plot for significance
indeks2 = find(p2<0.05);
AAA2(1,:)=nanmean(A3,1);
AAA2(2,:)=nanmean(B3,1);
AA2=nanmax(AAA2,[],1)+0.0001;
C2=zeros(size(AA2));  C2(indeks2)=1;
D2=AA2.*C2;    D2(D2==0)=NaN;

% errorbar
A3std = nanstd(A3);
B3std = nanstd(B3);
D2 = D2+max([A3std; B3std]);

% plot
ff=figure;
hold on;
plot1 = plot(from_plot:10:to_plot,nanmean(A3(:,18:40),1),'o-','Linewidth',3,'markersize',4,'Color','green');
errorbar(from_plot:10:to_plot,nanmean(A3(:,18:40),1),A3std(:,18:40),'ko-','Linewidth',2,'markersize',4,'Color','green'); hold on;
plot2 = plot(from_plot:10:to_plot,nanmean(B3(:,18:40),1),'ro-','Linewidth',3,'markersize',4,'Color','black');
errorbar(from_plot:10:to_plot,nanmean(B3(:,18:40),1),B3std(:,18:40),'ro-','Linewidth',2,'Color','black');

plot(from_plot:10:to_plot,D2(:,18:40),'k*','markersize',8,'LineWidth',1) 
plot(from_plot:10:to_plot,zeros(1,23),'k--')
set(gca,'Fontsize',14,'XGrid','on','XLim',[from_plot to_plot])

plot3 = [plot1,plot2];
LE = legend(plot3,{'cond_A'; 'cond_B'});
set(LE,'Interpreter','none','Fontsize',16)
set(gcf,'PaperPositionMode','auto')