This could be happening because of license checkout delays on the network.
Try to execute the following command to verify the time taken for license checkout: >> [status,errmsg] = license('checkout','matlab')
where 'matlab' could be replaced by any other toolbox too.
Once MATLAB is launched a MATLAB license is checked out until the MATLAB session is exited. In general, this also holds true for toolboxes. As soon as someone launches a MATLAB session and then uses a command from a toolbox, a toolbox license is checked out until the session of MATLAB is exited. For example, if a user launches MATLAB and then from the command line uses the command SINC, the user will have two licenses checked out: MATLAB and the Signal Processing Toolbox. Usually, these licenses will not be returned to the license pool until the user exits their session of MATLAB.