See: Failed to find object 'Class None.' - Pipeline & Plugins - Unreal Engine Forums
This one is going as far back as 2014 but I’m not sure if it is exactly the same bug:
Also I can not see the status of submitted bug reports. I do not know if this specific one was fixed or not.
Hi ,
I have moved your other thread to the bug reports section and have assigned someone to look at the error in question, please continue the conversation there. I am closing this thread as a duplicate.