When try to save or publish the workflow, this error might occurs:
ButtonPanel - handleXamlBuildError : SyntaxError: Invalid character
An error occurred that could be due to size of the workflow. Try reducing the size of your workflow. For example, reduce the size of task forms or split up the workflow.

Split the single workflow into multiple workflows. 

While there can be many causes for these errors, one of them can be when you have too many tasks in parallel in a single workflow. A large workflow has more tasks and more updates in the single workflow, so more chance of causing a lock. Also if a lock does occur, a larger workflow can make it difficult to determine the point at which the lock happened while a smaller workflow will always be easier to diagnose.