Only for One user n he got error on the My Workflow Tasks webpart.
the error is :
Error: The execution time has expired. The timeout has elapsed before the end of the operation or the server is not responding.
I delete all tasks for this user n but the error still .
I've same problem with web part Workflows I've Started.
I able to solve this issue by rebuild the index of workflow related table in NW2013DB.
You may refer to the link below: