August 14, 2020 and I am still encountering this in 4.25.3. I see UE-63064 that seems to be related or possibly claiming it is fixed, but this is absolutely not the case.
It looks to be related to renaming the graph node associated. I have documented the steps with images in the link below, but I will copy/paste the text steps as well.
Link: UE 4.25.3 - Cannot delete EventDispatcher - Album on Imgur
- Creating a new Event Dispatcher
- Selecting any function (pre-existing or an empty one). In this case, I setup a junk function with an input, but it does nothing.
- Confirm the inputs show up. (I had a single Bool for this empty function)
- Double clicking on the EventDispatcher entry in the left-hand pane to bring up the Event Graph.
NOTE: Up to this point, I can delete it. I can even back out with the graph open and delete the Event Dispatcher.
- I renamed the node from ‘New Event Dispatcher 0’ to ‘Renamed’.
- It’s now locked with ‘Delete’ greyed out.
- Attempting to compile produces the tragic messages:
No delegate property found for Renamed
No SignatureFunction in MulticastDelegateProperty 'NewEventDispatcher 0'