Hey ,
I understand, but at this point, there have been multiple fixes related to hot reloading put into 4.9 which were not integrated into 4.8. Since this is the case, I would suggest either upgrading to 4.9 or avoiding hot reload by closing the editor when you compile. Unfortunately, I can no longer be of assistance without a way to reproduce this unless we know that it is still occurring in 4.9.
Have a nice day,
I’m experiencing exactly the same problem on clean 4.9.1 with my blueprint, refreshing all nodes makes the error go away.
Ok, I was about to switch to 4.9.1 this week or the next…looks like this is still broken… , any update on your side? Anyone else noticed a similar behavior?
Hello ,
As we have been unable to reproduce these errors thus far, we are unable to proceed further in assisting with this issue.
Speaking of which, , if you’re having these issues, would it be possible to get a copy of the project that this is occurring in so that I could use it for a repro case?
Here you go:
.com//UnrealBlueprintProblems
I have cut it down to minimum I think. Just compile it from the editor, blueprint (MyUserWidgetBP) looks ok, but click compile - error.
There is also another problem in that project which I mention in below post, but its not as easy to reproduce:
Hello everyone,
Thank you for providing this project to help with the reproduction of the issue. I was able to get the issue to happen without a problem. I’ve placed a bug into our system for this issue. For your reference, the bug number is UE-21538.
I suggest using the refresh nodes functions for now until this can be resolved.
Have a nice day!
Thank you for this report and the fix! I had recently added DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam to one of my classes bodies and was happily coding for a long enough time that I didn’t know what could be causing the new hot reload issues. Once I moved the delegate declaration out of my class body the problem went away. This is in version 4.12.4 of the engine. You saved me a day or more of debugging, and for that I thank you! 
God it’s 4.17 and Epic STILL didnt touch this issue.
Thank you for your hard work at debugging this, your solution worked like magic.