How do I ensure that the number of delimiters on each row are constant when reading a hige csv file

That's the job of the writer of the file; do you have any control over that?

Is it possible the problem is that there are headers or multiple sections within the file that needs must be handled specifically? Or are there strings with embedded punctuation perhaps that weren't quote-delimited and that's causing interpretation as multiple fields?

So many possibilities, so little fact on which to work...as noted earlier, need to see a portion of the file that contains the problem to be able to know anything at all for sure.

You can always brute-force check, of course --

fid=fopen('yoursuspectfile.csv','r');  % open the file
l=fgetl(fid);                          % read first line
n1=sum(l==',');                        % count delimiters first record
i=1;                                   % record counter
disp(sprintf('Record %5d has %5d delimiters',i,n1))
while ~feof(fid)                       % rest of file
  i=i+1;                               % increment counter
  l=fgetl(fid);
  if sum(l==',')~=n1                   % not same as first record
    disp(sprintf('Record %5d has %5d delimiters',i,n1))
  end
end
fid=fclose(fid)