It is very likely that the problem is related to memory limitation or timeout on the workers. If some tasks are killed by the cluster, you won't be able to successfully fetch the results. Increase the quota values for memory and processing time. The follwoings work for my job.
Use appropriate settings for you job and do not set a very large WallTime, since it may delay your tasks in the queue. If you do not have these commands, download ClusterInfo from MATLAB File Exchange.