title: CoreML : "Unexpected error processing model" error sometimes occurring
body: <p><strong>Context:</strong>
  I'm using a custom CoreML model made by a datascientist.
  The model is a pipeline that uses Apple <code>SoundAnalysisPreprocessing</code> model as it's first model. <code>SoundAnalysisPreprocessing</code> model is followed by a custom model that contains different convolution layers and a softmax.</p>
  
  <p><strong>Issue:</strong>
  When launching a prediction, I sometimes get <code>Unexpected error processing model</code>. With the exact same input, I sometimes get a correct result and sometimes I get this error.</p>
  
  <p><strong>Question:</strong> I have no clue what to do with this error. Is it a memory problem with input being badly allocated ? Is it a problem with the model itself ?
  Do you have any idea what I could do to understand what is happening ?</p>
  
  <p><strong>Complete error log:</strong></p>
  
  <pre><code>[DSPGraph] throwing DSPGraph::Exception with backtrace:
  0       0x7fff2bcf5df9  DSPGraph::Graph::processMultiple(DSPGraph::GraphIOData*, DSPGraph::GraphIOData*) + 249
  1       0x7fff2bc3b570  processThroughGraph(id&lt;MLFeatureProvider&gt;, MLMultiArrayConstraint*, MLMultiArray*, NSString*, DSPGraph::Graph&amp;, std::__1::vector&lt;float, DSPGraph::Graph&amp;::allocator&lt;float&gt; &gt;&amp;, void (DSPGraph::Graph, NSString*::GraphIOData&amp;) block_pointer, NSError* __autoreleasing*) + 979
  2       0x7fff2bc3c573  -[SNDSPGraphCustomModel predictionFromFeatures:options:error:] + 195
  3       0x7fff2bc3ca49  -[_SNVGGishFrontEndProcessingCustomModel predictionFromFeatures:options:error:] + 98
  4       0x7fff2496ac30  -[MLAppleSoundAnalysisPreprocessing predictionFromFeatures:options:error:] + 132
  5       0x7fff248d345c  -[MLPipeline predictionFromFeatures:options:error:] + 178
  6       0x7fff24923f76  -[MLModel predictionFromFeatures:error:] + 92
  7          0x104b89a68  $s10TestCoreML17AudioFileAnalyzerC019previsionWithManualD3Cut33_1966162A0510E69792A8D979B37CC177LL3for10completiony10Foundation3URLV_ySo12MLMultiArrayCSgXEtF + 5992
  8          0x104b87850  $s10TestCoreML17AudioFileAnalyzerC05startF03for10completiony10Foundation3URLV_yyXEtF + 80
  9          0x104bb360c  $s10TestCoreML23ClassificationViewModelC14startRecognize4word8mockData11resultBlock06finishM0ySS_SbySb_SaySo16SNClassificationCGSgtcSgyyctF + 3436
  10         0x104bad21c  $s10TestCoreML18ReadViewControllerC010collectionE0_15didSelectItemAtySo012UICollectionE0C_10Foundation9IndexPathVtFyycfU_ + 220
  11         0x104b923fd  $sIeg_IeyB_TR + 45
  12         0x104f79d64  _dispatch_client_callout + 8
  13         0x104f7c6d6  _dispatch_continuation_pop + 552
  14         0x104f8fa8f  _dispatch_source_invoke + 2205
  15         0x104f87c53  _dispatch_main_queue_callback_4CF + 1043
  [truncated?]
  2019-10-30 20:33:04.209693+0100 TestCoreML[5024:191792] [] Caught graph exception 1718775073 !mrf fromBytePos (0) + numBytesToCopy (61440) &gt; mABL-&gt;mBuffers[0].mDataByteSize (2112) in /BuildRoot/Library/Caches/com.apple.xbs/Sources/Listen_Sim/Listen-35/CoreAudioUtility/Source/CADSP/DSPGraph/DSPGraph_Utils.cpp:742
  </code></pre>