One of our NW 2013 Request approval workflows wouldn't complete and the user asked me why. After a close look I told the guy that one more approver was expected to have their say.
The user then deleted the task that was unnecessary, but that didn't result in a successfully completed approval.
Then someone restored the task from the recycle bin and tried to delegate it and, BOOM, the workflow errored, all approvals must be requested once again?
w3wp.exe (0x1AF0) 0x869C Nintex
getting context data for 'WorkflowOwner'. --->
System.NullReferenceException: Object reference not set to an instance of an
object. at Microsoft.SharePoint.Workflow.SPWorkflow.get_OwnerUser()
Nintex.Workflow.NWWorkflowContext.VRw=(ContextDataOptions Vhw=, Boolean
Vxw=) --- End of inner exception stack trace --- (Build:3110)
I'm sure this is a valid support case, but maybe someone has already seen something like this and knows how to fix or prevent such issues going forward. At least you'll know that we have faced it already