I run into an error when I save a large workflow.
Situation: When I copy the 'Assign a task' action, this error happens. The image below demonstrates the error.
Is there any solutions?
Some previous questions of this nature suggest that IE/Edge can sometimes cause this issue on publishing (although the link here is in regards to a form, it's worth a try), so a quick first test might be to try it on Chrome/Firefox if you haven't already:
Object reference not set to an instance of an object
This could also be a result of copied variable references. If the 'Assign a Task' action you copied from contained variables in its configuration, it may be worth removing them from the config of the copied action and then manually re-adding them.
Let me know if the above get you anywhere,