It is likely that this issue is due to network licensing. To confirm this, try the following:
1) Locate the MLM_LICENSE_FILE environment variable, as specified here:
2) Copy the value of MLM_LICENSE_FILE up to ";" . It should be something like this:
27000@<servername>,27000@<servername>2,27000@<servername>3, where <servername> is set according to your organization name
3) Navigate to "<matlabroot>/bin" in the file explorer.
4) Right-click "matlab.EXE" and make a new desktop shortcut for it. Do not use an existing shortcut, as there may be permissions issues.
5) Right-click the shortcut and select "Properties".
6) In the Target field, add -c and then paste your previously copied values. It should look like this:
"C:\Program Files\MATLAB\R2019b\bin\matlab.exe" -c27000@<servername>,27000@<servername>2,27000@<servername>3
7) Click "Apply" and launch MATLAB from the shortcut.
This should resolve most issues with parallel pool. If using the -c option with the MLM_LICENSE_FILE did not seem to help, Please run the following command and send us the result at Technical Support.
>> tic; system_dependent('lmfeaturelist', 2); toc
This will time a special type of license check that occurs before parallel work.
If a startup.m is trying to open a prompt, it will cause a hang. The portions of the startup that are opening in a prompt can be enclosed in an if structure to correct this: