Why is Matlab giving an UndefinedFunction error in this parfor loop?

UPDATE: I decided to take the opportunity to update to R2018b, and the problem is gone. Who knows what caused it, but this problem is no longer a problem. Thanks if you were already thinking about it!

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I am having some trouble assigning values to a cell array inside a parfor loop. Here is what I think are the relevant parts of the script:

isoBins = cell(1,nBins);
parfor nBin = 1:nBins

    for ii = 1:iters
      %build a cell called isoClasses%
    end

    isoBins{nBin} = isoClasses;

end

Within the parfor, isoBins is only referenced once, at the end of each loop, exactly as shown above. It is initialized immediately before the parfor, also exactly as shown above. The code runs fine, with the expected results, when I replace 'parfor' with 'for'. But the parallel code throws:

Error using enumerateAllGraphs (line 87)
An UndefinedFunction error was thrown on the workers for 'isoBins'.  This might be because the
file containing 'isoBins' is not accessible on the workers.  Use addAttachedFiles(pool, files)
to specify the required files to be attached.  See the documentation for
'parallel.Pool/addAttachedFiles' for more details.
Caused by:
    Undefined function or variable 'isoBins'.

I have searched both here and on the broader web, and haven't found anything that helps; I tried building a minimal example and it doesn't throw the error. I'm at a complete loss, so anything will help. Thanks!

Just in case the full code is helpful, here it is:

% Parallelize isomorphism calculations
allSequenceBins = sequenceBins.values;
isoBins = cell(1,nBins);
% each isoBin cell contains isomorphism classes of one particular deg seq

parfor nBin = 1:nBins      % TODO: parfor

      fePairs = allSequenceBins{nBin};
      nPairs = numel(fePairs);
      isoClasses = {};

      for fePair = 1:nPairs

          % build G
          fe = fePairs{fePair};
          F = zeros(n);
          E = zeros(n);
          F(sub2ind([n,n],fe(1,:),1:n)) = 1;
          E(sub2ind([n,n],fe(2,:),1:n)) = 1;
          FE = F - E;
          G = digraph(FE);

          % check G against reps of each extant class
          nClasses = numel(isoClasses);
          placed = 0;     % when placed, set to 1 and break
          for nClass = 1:nClasses
              isoClass = isoClasses{nClass};
              repG = isoClass{1};
              if isisomorphic(repG,G,'EdgeVariables','Weight')
                  nInClass = numel(isoClass);
                  isoClass{nInClass+1} = G;
                  placed = 1;   
                  isoClasses{nClass} = isoClass;
                  break;
              end
          end
          if placed
              continue
          else
              isoClasses{nClasses+1} = {G};
          end

      end
      isoBins{nBin} = isoClasses;

end

[Richard Buckalew]

Update: I decided to poke around in my parallel settings a bit, and found some tests to run on my local cluster profile. The 'Job test' test seems to hang -- it's said "Running" for several minutes now. Maybe this is related?

[Walter Roberson]

(Richard updated MATLAB versions, which fixed the problem.)