Error on UART reception (Matlab), partial reading

Question

I've generated a FFT algorithm running on a Xilinx Artix7. At the end of the fft calculation the algorithm send data to a computer by UART connection. I've checked my output on FPGA board with a debugger , it's look perfectly fine. Still Matlab receive only partial data. If I generate successive slope for instance on 10 slopes 2 or 3 will be fine, during the rest of the time I have something looking like a noice.

If someone have ever encounter this issue, or have good use on Matlab UART com it will be helpful, here is my Matlab code:

s = serial('COM6');                                 %assigns the object s to serial port
 
set(s, 'InputBufferSize', 512);                    %number of bytes in inout buffer: you have the choice between several values : 128,256,512,1024;
set(s, 'FlowControl', 'hardware');
set(s, 'BaudRate', 115200);
set(s, 'Parity', 'none');
set(s, 'DataBits', 8);
set(s, 'StopBit', 1);
set(s, 'Timeout',10);
%clc;

disp(get(s,'Name'));
prop(1)=(get(s,'BaudRate'));
prop(2)=(get(s,'DataBits'));
prop(3)=(get(s, 'StopBit'));
prop(4)=(get(s, 'InputBufferSize'));
 
disp(['Port Setup Done!!',num2str(prop)]);
 
fopen(s);                                           %opens the serial port

disp('Running... waiting for datas...put the reset "off"');
x=0;
a =fread(s);                                        %reads the data from the serial port and stores it to the matrix a

x=[a];
disp('Courbe tracée!');
fclose(s);                                          %close the serial porty
plot(a)


%%traitement

a=a';

T = [0,255,0];%find this sequence



out = strfind(a,T)