Error in using trainNetwork with trainingOptions verbose as 'true'

Im trying to perform image classification on AlexNet. The network trains just fine. However, if I set the verbose to 'true' under the trainingOptions, I get an error as shown below. I cant find the source of the error. Any idea how to fix this error? or is there any other way I can save my training progress (accuracy or loss in every epochs) in a text file or some sort? Thank you.

options = trainingOptions('sgdm', ...
    'MiniBatchSize',7, ...
    'MaxEpochs',100, ...
    'InitialLearnRate',1e-4, ...
    'Shuffle','every-epoch', ...
    'ValidationData',imdsValidation, ...
    'ValidationFrequency',3, ...
    'Plots','training-progress',...
    'Verbose',false, ...
    'OutputFcn',@(info)stopIfAccuracyNotImproving(info,20));

imageAugmenter = imageDataAugmenter( ...
    'RandXReflection', true,...
    'RandYReflection', true);

augImds = augmentedImageDatastore(inputSize,imdsTrain, ...
    'DataAugmentation',imageAugmenter);

net = trainNetwork(augImds,layers,options);

Error using trainNetwork (line 165)

Invalid separator input: string

Error in Alexnet (line 134)

net = trainNetwork(augImds,layers,options);

Caused by:

Error using strjoin (line 37)

Invalid separator input: string

[Dheeraj Singh]

Can you provide the mat file of the variables, to reproduce the problem??